**UNITED STATES SECURITIES AND EXCHANGE COMMISSION**

**Washington, D.C. 20549**

 

**Form 10-K/A**

**(Amendment No. 2)**

 

**(Mark One)**

 

**x****      ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934**

 

**For the fiscal year ended December 31, 2012**

 

**or**

 

**o****         TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934**

 

**For the transition period from            to           **

 

**Commission file number 1-34736**

 

**SEMGROUP CORPORATION**

(Exact name of registrant as specified in its charter)

 

| **Delaware**   (State or other jurisdiction of   incorporation or organization) | ** ** | **20-3533152**  (I.R.S. Employer   Identification No.) |
|---------------------------------------------------------------------------------|------------|-------------------------------------------------------------|

 

**Two Warren Place**

**6120 S. Yale Avenue, Suite 700**

**Tulsa, OK  74136-4216**

**(918) 524-8100**

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

 

Securities registered pursuant to Section 12(b) of the Act:

 

| **Title of Each Class**                                                   | ** ** | **Name of Each Exchange on Which Registered** |
|------------------------------------------------------------------------------------------|------------|-----------------------------------------------------------------------------|
| Class A Common Stock, par value $0.01 per share   Warrants to Purchase Common Stock |       | New York Stock Exchange    New York Stock Exchange                          |

 

Securities registered pursuant to Section 12(g) of the Act:

**None**

 

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes x  No o

 

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes  o  No  x

 

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes  x  No  o

 

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). Yes x No o

 

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K (§229.405 of this chapter) is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.  x

 

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

 

| Large Accelerated Filer x      |   | Accelerated Filer  o              |
|-----------------------------------------------|--------|---------------------------------------------|
|                                          |   |                                        |
| Non-Accelerated Filer  o            |   | Smaller Reporting Company  o |
| (Do not check if a smaller reporting company) |   |                                        |

 

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes  o  No x

 

The aggregate market value of the registrant’s Class A and Class B common stock held by non-affiliates at June 29, 2012, was $1,326,413,230, based on the closing price of the Class A common stock on the New York Stock Exchange on June 29, 2012.

 

Indicate by check mark whether the registrant has filed all documents and reports required to be filed by Section 12, 13 or 15(d) of the Securities Exchange Act of 1934 subsequent to the distribution of securities under a plan confirmed by a court.  Yes  x  No o

 

At January 31, 2013, there were 41,930,289 shares of Class A Common Stock and 28,235 shares of Class B Common Stock outstanding.

 

**DOCUMENTS INCORPORATED BY REFERENCE**

 

Portions of the registrant’s Proxy Statement filed pursuant to Regulation 14A of the Securities Exchange Act of 1934, in connection with the registrant’s Annual Stockholders’ Meeting held on May 22, 2013, are incorporated by reference into Part III of this Form 10-K.

 

 

 

----

 

**Explanatory Note**

 

This Amendment No. 2 (“Amendment No. 2”) to the Registrant’s Annual Report on Form 10-K for the year ended December 31, 2012, filed with the Securities and Exchange Commission (the “SEC”) on March 1, 2013 (the “Form 10-K”), is being filed for the purpose of providing separate financial statements of NGL Energy Partners LP and NGL Supply, Inc. (collectively, “NGL Energy”) in accordance with Rule 3-09 of Regulation S-X.  As indicated in the Form 10-K, NGL Energy is an equity method investee in which the Registrant owns 9.1 million common units and a 6.42% interest in the general partner of NGL Energy.  NGL Energy’s fiscal year ends on March 31 of each year, and as such, NGL Energy’s financial statements for the fiscal year ended March 31, 2013 were not available until after the date the Form 10-K was filed and, accordingly, the Registrant is filing the required NGL Energy financial statements with this Amendment No. 2.  NGL Energy is solely responsible for the form and content of the NGL Energy financial statements provided herewith.

 

As required by the rules of the SEC, this Amendment No. 2 sets forth an amended “Item 15. Exhibits and Financial Statement Schedules” in its entirety and includes the new certifications from the Registrant’s chief executive officer and chief financial officer.

 

Except as expressly noted herein, this Amendment No. 2 speaks as of the original filing date of the Form 10-K, does not reflect events that may have occurred subsequent to the original filing date, and does not modify or update in any way disclosures made in the Form 10-K.

 

2

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**Item 15.*    Exhibits and Financial Statement Schedules***

 

(a)                                 (1)***                                *****Financial Statements.** The consolidated financial statements of the Registrant included in the Form 10-K filed with the SEC on March 1, 2013, as listed on page F-1 thereof, which follows the signature page thereto.

 

(2)                                 **Financial Statement Schedules.** All financial statement schedules are omitted as inapplicable or because the required information is contained in the financial statements or the notes thereto.

 

The financial statements of White Cliffs Pipeline, L.L.C., one of our equity method investees, are included in Amendment No. 1 to the Form 10-K of the Registrant filed with the SEC on March 1, 2013 as Exhibit 99.1 pursuant to Rule 3-09 of Regulation S-X.

 

The financial statements of NGL Energy Partners LP and NGL Supply, Inc., one of our equity method investees, are included in this filing as Exhibit 99.2 pursuant to Rule 3-09 of Regulation S-X.

 

(3)                                 **Exhibits****.** The following documents are included as exhibits to this Amendment No. 2. Those exhibits below incorporated by reference herein are indicated as such by the information supplied in the parenthetical thereafter. If no parenthetical appears after an exhibit, such exhibit is filed with this Amendment No. 2 or, except as otherwise noted, was filed with the Form 10-K of the Registrant filed on March 1, 2013 or with Amendment No.1 thereto.

 
| **Exhibit   Number** | ** ** | **Description**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|----------------------|------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 2.1                  |       | Fourth   Amended Joint Plan of Affiliated Debtors filed with the United States   Bankruptcy Court for the District of Delaware on October 27, 2009 (filed as   Exhibit 2.1 to our registration statement on Form 10, File No. 001-34736 (the   “Form 10”)).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 2.2                  |       | Contribution   Agreement dated August 31, 2011, among SemStream, L.P., a wholly-owned   subsidiary of SemGroup Corporation, NGL Supply Terminal Company LLC, NGL   Energy Partners LP and NGL Energy Holdings LLC (filed as Exhibit 2.1 to our   current report on Form 8-K dated November 1, 2011, filed November 4, 2011).                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 2.3                  |       | Second   Amended and Restated Limited Liability Company Agreement of NGL Energy   Holdings LLC (filed as Exhibit 2.2 to our current report on Form 8-K dated   November 1, 2011, filed November 4, 2011).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 2.4                  |       | First   Amended and Restated Registration Rights Agreement dated October 3, 2011,   among NGL Energy Partners LP, Hicks Oil & Hicksgas, Incorporated, NGL   Holdings, Inc., Krim2010, LLC, Infrastructure Capital Management, LLC,   Atkinson Investors, LLC, Stanley A. Bugh, Robert R. Foster, Brian K. Pauling,   Stanley D. Perry, Stephen D. Tuttle, Craig S. Jones, Daniel Post, Mark   McGinty, Sharra Straight, David Eastin, AO Energy, Inc., E. Osterman, Inc.,   E. Osterman Gas Service, Inc., E. Osterman Propane, Inc., Milford Propane,   Inc., Osterman Propane, Inc., Propane Gas, Inc., and Saveway Propane Gas   Service, Inc. (filed as Exhibit 2.3 to our current report on Form 8-K dated   November 1, 2011, filed November 4, 2011). |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 2.5                  |       | Amendment   No. 1 and Joinder to First Amended and Restated Registration Rights Agreement   dated November 1, 2011, between NGL Energy Holdings LLC and SemStream, L.P.   (filed as Exhibit 2.4 to our current report on Form 8-K dated November 1,   2011, filed November 4, 2011).                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 2.6                  |       | Contribution   Agreement, dated as of January 8, 2013, by and among SemGroup Corporation,   Rose Rock Midstream Holdings, LLC, Rose Rock Midstream GP, LLC, Rose Rock   Midstream, L.P. and Rose Rock Midstream Operating, L.L.C. (filed as Exhibit   2.1 to our current report on Form 8-K dated January 8, 2013, filed January   14, 2013).                                                                                                                                                                                                                                                                                                                                                                                                                    |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 3.1                  |       | Amended   and Restated Certificate of Incorporation, dated as of November 30, 2009, of SemGroup   Corporation (filed as Exhibit 3.1 to the Form 10).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |

 

3

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| 3.2    |   | Amended   and Restated Bylaws, dated as of October 28, 2011, of SemGroup Corporation   (filed as Exhibit 3.1 to our current report on Form 8-K dated October 28,   2011, filed October 28, 2011).                                                                                                                                                                  |
|--------|--------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 4.1    |   | Form   of stock certificate for our Class A Common Stock, par value $0.01 per share   (filed as Exhibit 4.1 to the Form 10).                                                                                                                                                                                                                                       |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 4.2    |   | Form   of stock certificate for our Class B Common Stock, par value $0.01 per share   (filed as Exhibit 4.2 to the Form 10).                                                                                                                                                                                                                                       |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 4.3    |   | Warrant   Agreement dated as of November 30, 2009, by and between SemGroup Corporation and   Mellon Investor Services, LLC (filed as Exhibit 4.3 to the Form 10).                                                                                                                                                                                                  |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 4.4    |   | Form   of warrant certificate (filed as Exhibit 4.4 to the Form 10).                                                                                                                                                                                                                                                                                               |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 4.5*   |   | First   Amendment to Warrant Agreement, dated as of November 1, 2012, by and   between SemGroup Corporation and Computershare Shareowner Services LLC   (successor-in-interest to Mellon Investor Services, LLC).                                                                                                                                             |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.1   |   | Credit   Agreement (the “Credit Facility”) dated as of June 17, 2011, among SemGroup   Corporation, as borrower, the lenders parties thereto from time to time, and   The Royal Bank of Scotland PLC, as Administrative Agent and Collateral Agent   (filed as Exhibit 10 to our current report on Form 8-K dated June 17, 2011,   filed June 21, 2011). |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.2   |   | Second   Amendment to the Credit Facility, dated as of September 19, 2011 (filed as   Exhibit 10 to our current report on Form 8-K, dated September 19, 2011, filed   September 23, 2011).                                                                                                                                                                         |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.3+  |   | SemGroup   Corporation Board of Directors Compensation Plan (filed as Exhibit 10.6 to   the Form 10).                                                                                                                                                                                                                                                              |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.4+  |   | SemGroup   Corporation Nonexecutive Directors’ Compensation Deferral Program (filed as   Exhibit 10.7 to the Form 10).                                                                                                                                                                                                                                        |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.5+  |   | SemGroup   Corporation Equity Incentive Plan (filed as Exhibit 10.8 to the Form 10).                                                                                                                                                                                                                                                                               |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.6+  |   | SemGroup   Corporation Equity Incentive Plan Form of Restricted Stock Award Agreement   for Directors (filed as Exhibit 10.9 to the Form 10).                                                                                                                                                                                                                      |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.7+  |   | Amendment   No. 1 to SemGroup Corporation Equity Incentive Plan Form of Restricted Stock   Award Agreement for Directors (filed as Exhibit 10.15 to the Form 10).                                                                                                                                                                                                  |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.8+  |   | SemGroup   Corporation Equity Incentive Plan Form of Restricted Stock Award Agreement   for executive officers and employees in the United States (filed as Exhibit   10.10 to the Form 10).                                                                                                                                                                       |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.9+  |   | Amendment   No. 1 to SemGroup Corporation Equity Incentive Plan Form of Restricted Stock   Award Agreement for executive officers and employees in the United States   (filed as Exhibit 10.16 to the Form 10).                                                                                                                                                    |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.10+ |   | Amendment   No. 2 to SemGroup Corporation Equity Incentive Plan Form of Restricted Stock   Award Agreement for executive officers and employees in the United States   (filed as Exhibit 10.10 to our annual report on Form 10-K for the fiscal year   ended December 31, 2011, filed February 29, 2012 (the “2011 Form 10-K”)).                         |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.11+ |   | Employment   Agreement dated as of November 30, 2009, by and among SemManagement, L.L.C.,   SemGroup Corporation and Norman J. Szydlowski (filed as Exhibit 10.11 to the   Form 10).                                                                                                                                                                               |

 

4

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| 10.12+ |   | Letter   Amendment dated March 18, 2010, by and among SemManagement, L.L.C., SemGroup   Corporation and Norman J. Szydlowski, amending the Employment Agreement dated   as of November 30, 2009 (filed as Exhibit 10.12 to the Form 10).                                                                                                                                                    |
|--------|--------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.13+ |   | Form   of Severance Agreement between SemGroup Corporation and each of its executive   officers other than Norman J. Szydlowski and David B. Gorte (filed as Exhibit   10.13 to the Form 10).                                                                                                                                                                                               |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.14+ |   | Form   of Amendment to Severance Agreement between SemGroup Corporation and certain   of its executive officers (filed as Exhibit 10.14 to the 2011 Form 10-K).                                                                                                                                                                                                                             |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.15+ |   | SemGroup   Corporation Equity Incentive Plan Form of Retention Award Agreement for   certain executive officers (filed as Exhibit 10.14 to the Form 10).                                                                                                                                                                                                                                    |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.16+ |   | SemGroup   Corporation Equity Incentive Plan Form of Restricted Stock Award Agreement   for Directors for awards granted on or after August 31, 2010 (filed as   Exhibit 10.17 to the Form 10).                                                                                                                                                                                             |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.17+ |   | SemGroup   Corporation Equity Incentive Plan Form of Restricted Stock Award Agreement   for executive officers and employees in the United States for awards granted   on or after August 31, 2010 (filed as Exhibit 10.18 to the Form 10).                                                                                                                                                 |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.18+ |   | Form   of 2011 Performance Share Unit Award Agreement under the SemGroup Corporation   Equity Incentive Plan for executive officers (filed as Exhibit 10.1 to our   current report on Form 8-K dated January 24, 2011, filed January 24, 2011).                                                                                                                                             |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.19+ |   | Form   of Restricted Stock Award Agreement under the SemGroup Corporation Equity   Incentive Plan for executive officers and employees in the United States   during 2011 (filed as Exhibit 10.2 to our current report on Form 8-K dated   January 24, 2011, filed January 24, 2011).                                                                                                       |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.20+ |   | Form   of 2012 Performance Share Unit Award Agreement under the SemGroup Corporation   Equity Incentive Plan for executive officers (filed as Exhibit 10.20 to the   2011 Form 10-K).                                                                                                                                                                                                       |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.21+ |   | Form   of Restricted Stock Award Agreement under the SemGroup Corporation Equity   Incentive Plan for executive officers and employees in the United States for   awards granted on or after January 1, 2012 (filed as Exhibit 10.21 to the   2011 Form 10-K).                                                                                                                              |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.22+ |   | SemGroup   Corporation Short-Term Incentive Program (filed as Exhibit 10.1 to our   current report on Form 8-K dated February 24, 2011, filed March 2, 2011).                                                                                                                                                                                                                               |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.23+ |   | Consulting   Services Agreement, effective as of February 2, 2012, by and between SemGroup   Corporation and David B. Gorte (filed as Exhibit 10.23 to the 2011 Form   10-K).                                                                                                                                                                                                               |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.24  |   | Credit   Agreement dated November 10, 2011, among Rose Rock Midstream, L.P., as   borrower, The Royal Bank of Scotland PLC, as administrative agent and collateral   agent, the other agents party thereto and the lenders and issuing banks party   thereto (filed as Exhibit 10.1 to Rose Rock Midstream, L.P.’s registration   statement on  Form S-1, File No.   333-176260). |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.25  |   | Second   Amended and Restated Agreement of Limited Partnership of Rose Rock Midstream,   L.P. (filed as Exhibit 3.1 to Rose Rock Midstream, L.P.’s current report on   Form 8-K dated December 14, 2011, filed December 20, 2011).                                                                                                                                                     |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.26  |   | First   Amended and Restated Limited Liability Company Agreement of Rose Rock   Midstream GP, LLC (filed as Exhibit 3.2 to Rose Rock Midstream, L.P.’s   current report on Form 8-K dated December 14, 2011, filed December 20, 2011).                                                                                                                                                 |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                        |
| 10.27+ |   | Rose   Rock Midstream Equity Incentive Plan (filed as Exhibit 10.1 to Rose Rock Midstream,   L.P.’s current report on Form 8-K dated December 8, 2011, filed December 14,   2011).                                                                                                                                                                                                     |

 

5

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| 10.28+  |   | Form   of Restricted Unit Award Agreement (Employees) under the Rose Rock Midstream   Equity Incentive Plan (filed as Exhibit 10.3.1 to Rose Rock Midstream, L.P.’s   annual report on Form 10-K for the fiscal year ended December 31, 2011, filed   February 29, 2012).                                                                                                                                                                                                                                                                                                          |
|---------|--------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 10.29   |   | Fifth   Amendment to the Credit Facility, dated as of September 26, 2012 (filed as   Exhibit 10.1 to our quarterly report on Form 10-Q for the quarter ended   September 30, 2012, filed November 9, 2012).                                                                                                                                                                                                                                                                                                                                                                             |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 10.30   |   | First   Amendment, dated as of September 26, 2012, to the Credit Agreement among Rose   Rock Midstream, L.P., certain subsidiaries of Rose Rock Midstream, L.P., as   guarantors, the lenders party thereto and The Royal Bank of Scotland plc, as   administrative agent and collateral agent for the lenders (filed as Exhibit   10.2 to our quarterly report on Form 10-Q for the quarter ended September 30,   2012, filed November 9, 2012).                                                                                                                                       |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 10.31+* |   | SemGroup   Corporation Equity Incentive Plan Form of Restricted Stock Award Agreement   for Directors for awards granted on or after May 22, 2012.                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 10.32   |   | Amendment   No. 1 to the Second Amended and Restated Agreement of Limited Partnership of   Rose Rock Midstream, L.P. (filed as Exhibit 3.1 to Rose Rock Midstream,   L.P.’s current report on Form 8-K dated January 8, 2013, filed January 14,   2013).                                                                                                                                                                                                                                                                                                                           |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 10.33+* |   | SemGroup   Corporation Equity Incentive Plan Form of Restricted Stock Award Agreement   for executive officers and employees in the United States for awards granted   on or after March 1, 2013.                                                                                                                                                                                                                                                                                                                                                                                       |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 10.34+* |   | SemGroup   Corporation Equity Incentive Plan Form of Performance Share Unit Award   Agreement for executive officers for awards granted on or after March 1,   2013.                                                                                                                                                                                                                                                                                                                                                                                                                    |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 10.35+* |   | Form   of restricted Unit Award Agreement (Employees) under the Rose Rock Midstream   Equity Incentive Plan for awards granted on or after March 1, 2013.                                                                                                                                                                                                                                                                                                                                                                                                                               |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 21*     |   | Subsidiaries   of SemGroup Corporation.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 23.1*   |   | Consent   of Independent Registered Public Accounting Firm — BDO USA, LLP.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 23.2**  |   | Consent   of Independent Registered Public Accounting Firm — Grant Thornton LLP.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 31.1**  |   | Rule   13a - 14(a)/15d - 14(a) Certification of Norman J. Szydlowski, Chief   Executive Officer.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 31.2**  |   | Rule   13a - 14(a)/15d - 14(a) Certification of Robert N. Fitzgerald, Chief   Financial Officer.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 32.1**  |   | Section   1350 Certification of Norman J. Szydlowski, Chief Executive Officer.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 32.2**  |   | Section   1350 Certification of Robert N. Fitzgerald, Chief Financial Officer.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 99.1*   |   | White   Cliffs Pipeline, L.L.C. financial statements presented pursuant to Rule 3-09   of Regulation S-X.                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 99.2**  |   | NGL   Energy Partners LP and NGL Supply, Inc. financial statements presented   pursuant to Rule 3-09 of Regulation S-X.                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 101*    |   | Interactive   data files pursuant to Rule 405 of Regulation S-T: (i) the Consolidated   Balance Sheets at December 31, 2012 and 2011, (ii) the Consolidated   Statements of Operations and Comprehensive Income (Loss) for the years ended   December 31, 2012, 2011 and 2010, (iii) the Consolidated Statements of   Changes in Owners’ Equity (Deficit) for the years ended December 31, 2012,   2011 and 2010, (iv) the Consolidated Statements of Cash Flows for the years   ended December 31, 2012, 2011 and 2010, and (v) the Notes to Consolidated   Financial Statements. |

 

6

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| *  |   | Previously   filed with the Form 10-K of the Registrant filed on March 1, 2013 or with   Amendment No.1 thereto. |
|----|--------|------------------------------------------------------------------------------------------------------------------|
| ** |   | Filed   or furnished, as applicable, with this Amendment No. 2.                                                  |
| +  |   | Management   contract or compensatory plan or arrangement.                                                       |

 

7

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**SIGNATURES**

 

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

 
|                      | SEMGROUP   CORPORATION      |
|---------------------------|-----------------------------|
| Date:  June 14, 2013 |                        |
|                      | By:                         | /s/   Robert N. Fitzgerald |
|                      | Robert   N. Fitzgerald      |
|                      | Senior   Vice President and |
|                      | Chief   Financial Officer   |

 

8

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**Index to Exhibits**

 

**The following documents are included as exhibits to this Amendment No. 2. Those exhibits below incorporated by reference herein are indicated as such by the information supplied in the parenthetical thereafter. If no parenthetical appears after an exhibit, such exhibit is filed with this Amendment No. 2 or, except as otherwise noted, was filed with the Form 10-K of the Registrant filed on March 1, 2013 or with Amendment No. 1 thereto.**

 
| **Exhibit   Number** | ** ** | **Description**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|----------------------|------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 2.1                  |       | Fourth   Amended Joint Plan of Affiliated Debtors filed with the United States   Bankruptcy Court for the District of Delaware on October 27, 2009 (filed as   Exhibit 2.1 to our registration statement on Form 10, File No. 001-34736 (the   “Form 10”)).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 2.2                  |       | Contribution   Agreement dated August 31, 2011, among SemStream, L.P., a wholly-owned   subsidiary of SemGroup Corporation, NGL Supply Terminal Company LLC, NGL   Energy Partners LP and NGL Energy Holdings LLC (filed as Exhibit 2.1 to our   current report on Form 8-K dated November 1, 2011, filed November 4, 2011).                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 2.3                  |       | Second   Amended and Restated Limited Liability Company Agreement of NGL Energy   Holdings LLC (filed as Exhibit 2.2 to our current report on Form 8-K dated   November 1, 2011, filed November 4, 2011).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 2.4                  |       | First   Amended and Restated Registration Rights Agreement dated October 3, 2011,   among NGL Energy Partners LP, Hicks Oil & Hicksgas, Incorporated, NGL   Holdings, Inc., Krim2010, LLC, Infrastructure Capital Management, LLC,   Atkinson Investors, LLC, Stanley A. Bugh, Robert R. Foster, Brian K. Pauling,   Stanley D. Perry, Stephen D. Tuttle, Craig S. Jones, Daniel Post, Mark   McGinty, Sharra Straight, David Eastin, AO Energy, Inc., E. Osterman, Inc.,   E. Osterman Gas Service, Inc., E. Osterman Propane, Inc., Milford Propane,   Inc., Osterman Propane, Inc., Propane Gas, Inc., and Saveway Propane Gas   Service, Inc. (filed as Exhibit 2.3 to our current report on Form 8-K dated   November 1, 2011, filed November 4, 2011). |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 2.5                  |       | Amendment   No. 1 and Joinder to First Amended and Restated Registration Rights Agreement   dated November 1, 2011, between NGL Energy Holdings LLC and SemStream, L.P.   (filed as Exhibit 2.4 to our current report on Form 8-K dated November 1,   2011, filed November 4, 2011).                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 2.6                  |       | Contribution   Agreement, dated as of January 8, 2013, by and among SemGroup Corporation,   Rose Rock Midstream Holdings, LLC, Rose Rock Midstream GP, LLC, Rose Rock   Midstream, L.P. and Rose Rock Midstream Operating, L.L.C. (filed as Exhibit   2.1 to our current report on Form 8-K dated January 8, 2013, filed January   14, 2013).                                                                                                                                                                                                                                                                                                                                                                                                                    |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 3.1                  |       | Amended   and Restated Certificate of Incorporation, dated as of November 30, 2009, of SemGroup   Corporation (filed as Exhibit 3.1 to the Form 10).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 3.2                  |       | Amended   and Restated Bylaws, dated as of October 28, 2011, of SemGroup Corporation   (filed as Exhibit 3.1 to our current report on Form 8-K dated October 28,   2011, filed October 28, 2011).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 4.1                  |       | Form   of stock certificate for our Class A Common Stock, par value $0.01 per share   (filed as Exhibit 4.1 to the Form 10).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 4.2                  |       | Form   of stock certificate for our Class B Common Stock, par value $0.01 per share   (filed as Exhibit 4.2 to the Form 10).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|                 |       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| 4.3                  |       | Warrant   Agreement dated as of November 30, 2009, by and between SemGroup Corporation and   Mellon Investor Services, LLC (filed as Exhibit 4.3 to the Form 10).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |

 

9

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| 4.4    |   | Form   of warrant certificate (filed as Exhibit 4.4 to the Form 10).                                                                                                                                                                                                                                                                                               |
|--------|--------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 4.5*   |   | First   Amendment to Warrant Agreement, dated as of November 1, 2012, by and   between SemGroup Corporation and Computershare Shareowner Services LLC   (successor-in-interest to Mellon Investor Services, LLC).                                                                                                                                             |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.1   |   | Credit   Agreement (the “Credit Facility”) dated as of June 17, 2011, among SemGroup   Corporation, as borrower, the lenders parties thereto from time to time, and   The Royal Bank of Scotland PLC, as Administrative Agent and Collateral Agent   (filed as Exhibit 10 to our current report on Form 8-K dated June 17, 2011,   filed June 21, 2011). |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.2   |   | Second   Amendment to the Credit Facility, dated as of September 19, 2011 (filed as   Exhibit 10 to our current report on Form 8-K, dated September 19, 2011, filed   September 23, 2011).                                                                                                                                                                         |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.3+  |   | SemGroup   Corporation Board of Directors Compensation Plan (filed as Exhibit 10.6 to   the Form 10).                                                                                                                                                                                                                                                              |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.4+  |   | SemGroup   Corporation Nonexecutive Directors’ Compensation Deferral Program (filed as   Exhibit 10.7 to the Form 10).                                                                                                                                                                                                                                        |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.5+  |   | SemGroup   Corporation Equity Incentive Plan (filed as Exhibit 10.8 to the Form 10).                                                                                                                                                                                                                                                                               |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.6+  |   | SemGroup   Corporation Equity Incentive Plan Form of Restricted Stock Award Agreement   for Directors (filed as Exhibit 10.9 to the Form 10).                                                                                                                                                                                                                      |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.7+  |   | Amendment   No. 1 to SemGroup Corporation Equity Incentive Plan Form of Restricted Stock   Award Agreement for Directors (filed as Exhibit 10.15 to the Form 10).                                                                                                                                                                                                  |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.8+  |   | SemGroup   Corporation Equity Incentive Plan Form of Restricted Stock Award Agreement   for executive officers and employees in the United States (filed as Exhibit   10.10 to the Form 10).                                                                                                                                                                       |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.9+  |   | Amendment   No. 1 to SemGroup Corporation Equity Incentive Plan Form of Restricted Stock   Award Agreement for executive officers and employees in the United States   (filed as Exhibit 10.16 to the Form 10).                                                                                                                                                    |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.10+ |   | Amendment   No. 2 to SemGroup Corporation Equity Incentive Plan Form of Restricted Stock   Award Agreement for executive officers and employees in the United States   (filed as Exhibit 10.10 to our annual report on Form 10-K for the fiscal year   ended December 31, 2011, filed February 29, 2012 (the “2011 Form 10-K”)).                         |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.11+ |   | Employment   Agreement dated as of November 30, 2009, by and among SemManagement, L.L.C.,   SemGroup Corporation and Norman J. Szydlowski (filed as Exhibit 10.11 to the   Form 10).                                                                                                                                                                               |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.12+ |   | Letter   Amendment dated March 18, 2010, by and among SemManagement, L.L.C., SemGroup   Corporation and Norman J. Szydlowski, amending the Employment Agreement dated   as of November 30, 2009 (filed as Exhibit 10.12 to the Form 10).                                                                                                                           |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.13+ |   | Form   of Severance Agreement between SemGroup Corporation and each of its executive   officers other than Norman J. Szydlowski and David B. Gorte (filed as Exhibit   10.13 to the Form 10).                                                                                                                                                                      |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.14+ |   | Form   of Amendment to Severance Agreement between SemGroup Corporation and certain   of its executive officers (filed as Exhibit 10.14 to the 2011 Form 10-K).                                                                                                                                                                                                    |
|   |   |                                                                                                                                                                                                                                                                                                                                                               |
| 10.15+ |   | SemGroup   Corporation Equity Incentive Plan Form of Retention Award Agreement for   certain executive officers (filed as Exhibit 10.14 to the Form 10).                                                                                                                                                                                                           |

 

10

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| 10.16+ |   | SemGroup   Corporation Equity Incentive Plan Form of Restricted Stock Award Agreement   for Directors for awards granted on or after August 31, 2010 (filed as   Exhibit 10.17 to the Form 10).                                                                                                                                                                                                                                                   |
|--------|--------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.17+ |   | SemGroup   Corporation Equity Incentive Plan Form of Restricted Stock Award Agreement   for executive officers and employees in the United States for awards granted   on or after August 31, 2010 (filed as Exhibit 10.18 to the Form 10).                                                                                                                                                                                                       |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.18+ |   | Form   of 2011 Performance Share Unit Award Agreement under the SemGroup Corporation   Equity Incentive Plan for executive officers (filed as Exhibit 10.1 to our   current report on Form 8-K dated January 24, 2011, filed January 24, 2011).                                                                                                                                                                                                   |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.19+ |   | Form   of Restricted Stock Award Agreement under the SemGroup Corporation Equity   Incentive Plan for executive officers and employees in the United States   during 2011 (filed as Exhibit 10.2 to our current report on Form 8-K dated   January 24, 2011, filed January 24, 2011).                                                                                                                                                             |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.20+ |   | Form   of 2012 Performance Share Unit Award Agreement under the SemGroup Corporation   Equity Incentive Plan for executive officers (filed as Exhibit 10.20 to the   2011 Form 10-K).                                                                                                                                                                                                                                                             |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.21+ |   | Form   of Restricted Stock Award Agreement under the SemGroup Corporation Equity   Incentive Plan for executive officers and employees in the United States for   awards granted on or after January 1, 2012 (filed as Exhibit 10.21 to the   2011 Form 10-K).                                                                                                                                                                                    |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.22+ |   | SemGroup   Corporation Short-Term Incentive Program (filed as Exhibit 10.1 to our   current report on Form 8-K dated February 24, 2011, filed March 2, 2011).                                                                                                                                                                                                                                                                                     |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.23+ |   | Consulting   Services Agreement, effective as of February 2, 2012, by and between SemGroup   Corporation and David B. Gorte (filed as Exhibit 10.23 to the 2011 Form   10-K).                                                                                                                                                                                                                                                                     |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.24  |   | Credit   Agreement dated November 10, 2011, among Rose Rock Midstream, L.P., as   borrower, The Royal Bank of Scotland PLC, as administrative agent and   collateral agent, the other agents party thereto and the lenders and issuing   banks party thereto (filed as Exhibit 10.1 to Rose Rock Midstream, L.P.’s   registration statement on  Form S-1,   File No. 333-176260).                                                       |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.25  |   | Second   Amended and Restated Agreement of Limited Partnership of Rose Rock Midstream,   L.P. (filed as Exhibit 3.1 to Rose Rock Midstream, L.P.’s current report on   Form 8-K dated December 14, 2011, filed December 20, 2011).                                                                                                                                                                                                           |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.26  |   | First   Amended and Restated Limited Liability Company Agreement of Rose Rock   Midstream GP, LLC (filed as Exhibit 3.2 to Rose Rock Midstream, L.P.’s   current report on Form 8-K dated December 14, 2011, filed December 20, 2011).                                                                                                                                                                                                       |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.27+ |   | Rose   Rock Midstream Equity Incentive Plan (filed as Exhibit 10.1 to Rose Rock   Midstream, L.P.’s current report on Form 8-K dated December 8, 2011, filed   December 14, 2011).                                                                                                                                                                                                                                                           |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.28+ |   | Form   of Restricted Unit Award Agreement (Employees) under the Rose Rock Midstream   Equity Incentive Plan (filed as Exhibit 10.3.1 to Rose Rock Midstream, L.P.’s   annual report on Form 10-K for the fiscal year ended December 31, 2011, filed   February 29, 2012).                                                                                                                                                                    |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.29  |   | Fifth   Amendment to the Credit Facility, dated as of September 26, 2012 (filed as   Exhibit 10.1 to our quarterly report on Form 10-Q for the quarter ended   September 30, 2012, filed November 9, 2012).                                                                                                                                                                                                                                       |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 10.30  |   | First   Amendment, dated as of September 26, 2012, to the Credit Agreement among Rose   Rock Midstream, L.P., certain subsidiaries of Rose Rock Midstream, L.P., as   guarantors, the lenders party thereto and The Royal Bank of Scotland plc, as   administrative agent and collateral agent for the lenders (filed as Exhibit   10.2 to our quarterly report on Form 10-Q for the quarter ended September 30,   2012, filed November 9, 2012). |

 

11

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| 10.31+* |   | SemGroup   Corporation Equity Incentive Plan Form of Restricted Stock Award Agreement   for Directors for awards granted on or after May 22, 2012.                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|---------|--------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 10.32   |   | Amendment   No. 1 to the Second Amended and Restated Agreement of Limited Partnership of   Rose Rock Midstream, L.P. (filed as Exhibit 3.1 to Rose Rock Midstream,   L.P.’s current report on Form 8-K dated January 8, 2013, filed January 14,   2013).                                                                                                                                                                                                                                                                                                                           |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 10.33+* |   | SemGroup   Corporation Equity Incentive Plan Form of Restricted Stock Award Agreement   for executive officers and employees in the United States for awards granted   on or after March 1, 2013.                                                                                                                                                                                                                                                                                                                                                                                       |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 10.34+* |   | SemGroup   Corporation Equity Incentive Plan Form of Performance Share Unit Award   Agreement for executive officers for awards granted on or after March 1,   2013.                                                                                                                                                                                                                                                                                                                                                                                                                    |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 10.35+* |   | Form   of restricted Unit Award Agreement (Employees) under the Rose Rock Midstream   Equity Incentive Plan for awards granted on or after March 1, 2013.                                                                                                                                                                                                                                                                                                                                                                                                                               |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 21*     |   | Subsidiaries   of SemGroup Corporation.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 23.1*   |   | Consent   of Independent Registered Public Accounting Firm — BDO USA, LLP.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 23.2**  |   | Consent   of Independent Registered Public Accounting Firm — Grant Thornton LLP.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 31.1**  |   | Rule   13a - 14(a)/15d - 14(a) Certification of Norman J. Szydlowski, Chief   Executive Officer.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 31.2**  |   | Rule   13a - 14(a)/15d - 14(a) Certification of Robert N. Fitzgerald, Chief   Financial Officer.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 32.1**  |   | Section   1350 Certification of Norman J. Szydlowski, Chief Executive Officer.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 32.2**  |   | Section   1350 Certification of Robert N. Fitzgerald, Chief Financial Officer.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 99.1*   |   | White   Cliffs Pipeline, L.L.C. financial statements presented pursuant to Rule 3-09   of Regulation S-X.                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 99.2**  |   | NGL   Energy Partners LP and NGL Supply, Inc. financial statements presented   pursuant to Rule 3-09 of Regulation S-X.                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| 101*    |   | Interactive   data files pursuant to Rule 405 of Regulation S-T: (i) the Consolidated   Balance Sheets at December 31, 2012 and 2011, (ii) the Consolidated   Statements of Operations and Comprehensive Income (Loss) for the years ended   December 31, 2012, 2011 and 2010, (iii) the Consolidated Statements of   Changes in Owners’ Equity (Deficit) for the years ended December 31, 2012,   2011 and 2010, (iv) the Consolidated Statements of Cash Flows for the years   ended December 31, 2012, 2011 and 2010, and (v) the Notes to Consolidated   Financial Statements. |
|    |   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |

----

| *  |   | Previously   filed with the Form 10-K of the Registrant filed on March 1, 2013 or with   Amendment No. 1 thereto. |
|----|--------|-------------------------------------------------------------------------------------------------------------------|
| ** |   | Filed   or furnished, as applicable, with this Amendment No. 2.                                                   |
| +  |   | Management   contract or compensatory plan or arrangement.                                                        |

 

12

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