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| (Mark One)                                        |   |   |
| ý                                            |   | ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 |
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| For the fiscal year ended: December 31, 2017 |
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| o                                                 |   | TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 |

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| Delaware(State or other jurisdiction of incorporation)                                                                    |   | 33-0968580(IRS Employer Identification No.) |
|                                                                                                                      |   |   |
| 4675 MacArthur Court, Suite 800, Newport Beach, CA 92660(Address of principal executive offices, including zip code) |
|                                                                                                                      |
| (949) 437-1000(Registrant's telephone number, including area code)                                                   |

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| Title of each class                       |   | Name of each exchange on which registered |
| Common Stock, par value $0.0001 per share |   | The Nasdaq Stock Market |

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| Large accelerated filer  o |   | Accelerated filer x |   | Non-accelerated filer o (Do not check if a smallerreporting company) |   | Smaller reporting company o |   | Emerging growth company o |

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| Report of Independent Registered Public Accounting Firm |
| Consolidated Balance Sheets                             |
| Consolidated Statements of Operations                   |
| Consolidated Statements of Comprehensive Loss           |
| Consolidated Statements of Stockholders' Equity         |
| Consolidated Statements of Cash Flows                   |
| Notes to Consolidated Financial Statements              |

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|                                      |  |  |  |  |  |  |  |  |
|                                 | (In thousands) |   |
|                                 | Allowances forDoubtful TradeReceivables |   | Allowance forDoubtful NotesReceivables |   |
| Balance as of December 31, 2014 | $ | 752 |  |   | $ | 2,850 |  |   |
| Charges (benefit) to operations      | 1,514 |  |   | 1,142 |  |   |
| Deductions                           | (371 | ) |   | (2 | ) |   |
| Balance as of December 31, 2015 | 1,895 |  |   | 3,990 |  |   |
| Charges (benefit) to operations      | 1,107 |  |   | 1,617 |  |   |
| Deductions                           | (1,939 | ) |   | (4,377 | ) |   |
| Balance as of December 31, 2016 | 1,063 |  |   | 1,230 |  |   |
| Charges (benefit) to operations      | 395 |  |   | 3,344 |  |   |
| Deductions                           | (182 | ) |   | (30 | ) |   |
| Balance as of December 31, 2017 | $ | 1,276 |  |   | $ | 4,544 |  |   |

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|               |
|---------------|
|               |  |  |  |  |  |  |
| ExhibitNumber |   |   |   | Incorporated herein by reference to the following filings: |
|          | Description |   | Form |   | Filed on |
| 2.11§    |   | Asset Purchase Agreement dated February 27, 2017, by and among Clean Energy Renewable Fuels, LLC, BP Products North America, Inc. and, solely with respect to Article VIII thereof, Clean Energy and BP Corporation North America, Inc. |   | Filed as Exhibit 2.11 to the Current Report on Form 8-K. |   | March 1, 2017 |
|          |   |   |   |   |   |   |
| 2.12          |   | Investment Agreement dated November 26, 2017, by and between Clean Energy and Landi Renzo S.p.A. |   | Filed as Exhibit 2.12 to the Current Report on Form 8-K. |   | November 27, 2017 |
|          |   |   |   |   |   |   |
| 3.1           |   | Restated Certificate of Incorporation, as amended by the Certificate of Amendment to the Restated Certificate of Incorporation of the Registrant dated May 28, 2010, as further amended by the Certificate of Amendment to the Restated Certificate of Incorporation of the Registrant dated May 8, 2014. |   | Filed as Exhibit 3.1.2 to the Quarterly Report on Form 10-Q for the quarter ended June 30, 2014. |   | August 7, 2014 |
|          |   |   |   |   |   |   |
| 3.2           |   | Amended and Restated Bylaws. |   | Filed as Exhibit 3.2 to the Current Report on Form 8-K. |   | February 23, 2011 |
|          |   |   |   |   |   |   |
| 3.2.1         |   | Amendment No. 1 to Amended and Restated Bylaws. |   | Filed as Exhibit 3.2.1 to the Current Report on Form 8-K. |   | February 27, 2014 |
|          |   |   |   |   |   |   |
| 4.1           |   | Specimen Common Stock Certificate. |   | Filed as Exhibit 4.1 to the Registration Statement on Form S-1, as amended. |   | March 27, 2007 |
|          |   |   |   |   |   |   |
| 4.10          |   | Form of Replacement Note issued by the Registrant. |   | Filed as Exhibit 4.9 to the Current Report on Form 8-K. |   | June 18, 2013 |
|          |   |   |   |   |   |   |
| 4.11          |   | Indenture dated September 16, 2013, between the Registrant and U.S. Bank National Association. |   | Filed as Exhibit 4.11 to the Current Report on Form 8-K. |   | September 16, 2013 |
|          |   |   |   |   |   |   |
| 4.12          |   | Form of 5.25% Convertible Senior Note due 2018. |   | Included with Exhibit 4.11 to the Current Report on Form 8-K. |   | September 16, 2013 |
|          |   |   |   |   |   |   |
| 10.4+         |   | Form of Indemnification Agreement. |   | Filed as Exhibit 10.4 to the Registration Statement on Form S-1, as amended. |   | March 27, 2007 |
|          |   |   |   |   |   |   |
| 10.7+         |   | 2006 Equity Incentive Plan—Form of Notice of Stock Option Grant and Stock Option Agreement. |   | Filed as Exhibit 99.5 to the Registration Statement on Form S-8. |   | August 14, 2007 |
|          |   |   |   |   |   |   |
| 10.12†  |   | Ground Lease dated November 3, 2006 among the Registrant, Clean Energy Construction and U.S. Borax, Inc. |   | Filed as Exhibit 10.25 to the Registration Statement on Form S-1, as amended. |   | May 24, 2007 |
|          |   |   |   |   |   |   |
| 10.16+        |   | 2006 Equity Incentive Plan—Form of Stock Award Agreement. |   | Filed as Exhibit 10.2 to the Quarterly Report on Form 10-Q for the quarter ended March 31, 2008. |   | May 15, 2008 |
|          |   |   |   |   |   |   |
| 10.63+        |   | Amended and Restated 2006 Equity Incentive Plan. |   | Filed as Exhibit 10.63 to the Annual Filing on Form 10-K for the fiscal year ended 2011. |   | March 12, 2012 |
| 10.64+        |   | Amended and Restated 2006 Equity Incentive Plan—Form of Notice of Stock Unit Award and Stock Unit Agreement. |   | Filed as Exhibit 10.64 to the Annual Filing on Form 10-K for the fiscal year ended 2011. |   | March 12, 2012 |
|          |   |   |   |   |   |   |
| 10.80         |   | Lease dated March 18, 2013, between The Irvine Company LLC and Clean Energy. |   | Filed as Exhibit 10.80 to the Quarterly Report on Form 10-Q for the quarter ended March 31, 2013. |   | May 8, 2013 |
|          |   |   |   |   |   |   |

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|               |
|---------------|
|               |  |  |  |  |  |  |
| ExhibitNumber |   |   |   | Incorporated herein by reference to the following filings: |
|          | Description |   | Form |   | Filed on |
| 10.81         |   | First Amendment to Lease dated April 17, 2013, between The Irvine Company LLC and Clean Energy. |   | Filed as Exhibit 10.81 to the Quarterly Report on Form 10-Q for the quarter ended March 31, 2013. |   | May 8, 2013 |
|          |   |   |   |   |   |   |
| 10.83         |   | Note Purchase Agreement dated June 14, 2013, among the Registrant, Chesapeake NG Ventures Corporation, Boone Pickens and Green Energy Investment Holdings, LLC. |   | Filed as Exhibit 10.83 to the Current Report on Form 8-K. |   | June 18, 2013 |
|          |   |   |   |   |   |   |
| 10.84         |   | Loan Agreement dated June 14, 2013, between the Registrant and Green Energy Investment Holdings, LLC. |   | Filed as Exhibit 10.84 to the Current Report on Form 8-K. |   | June 18, 2013 |
|          |   |   |   |   |   |   |
| 10.85         |   | Loan Agreement dated June 14, 2013, between the Registrant and Boone Pickens. |   | Filed as Exhibit 10.85 to the Current Report on Form 8-K. |   | June 18, 2013 |
|          |   |   |   |   |   |   |
| 10.86         |   | Registration Rights Agreement dated June 14, 2013, among the Registrant, Boone Pickens and Green Energy Investment Holdings, LLC. |   | Filed as Exhibit 10.86 to the Current Report on Form 8-K. |   | June 18, 2013 |
|          |   |   |   |   |   |   |
| 10.87         |   | Marketing Agreement dated June 28, 2013, among Clean Energy, Westport Power Inc. and Westport Fuel Systems Inc. |   | Filed as Exhibit 10.87 to the Current Report on Form 8-K. |   | June 28, 2013 |
|          |   |   |   |   |   |   |
| 10.90+        |   | Clean Energy Fuels Corp. Employee Stock Purchase Plan. |   | Filed as Exhibit Annex A to Schedule 14A Definitive Proxy Statement. |   | March 28, 2013 |
|          |   |   |   |   |   |   |
| 10.92†  |   | Liquefied Natural Gas Fueling Station and LNG Master Sales Agreement dated August 2, 2010, between Clean Energy and Pilot Travel Centers, LLC. |   | Filed as Exhibit 10.92 to the Annual Report on Form 10-K for the year ended December 31, 2013. |   | February 27, 2014 |
|          |   |   |   |   |   |   |
| 10.94         |   | Form of Common Unit Purchase Agreement dated October 14, 2014, among NG Advantage, LLC, Clean Energy and the other investors named therein. |   | Filed as Exhibit 10.94 to the Current Report on Form 8-K. |   | October 15, 2014 |
|          |   |   |   |   |   |   |
| 10.103+       |   | Amended and Restated 2006 Equity Incentive Plan - Form of Notice of Stock Unit Award. |   | Filed as Exhibit 10.103 to the Quarterly Report on Form 10‐Q for the quarter ended March 30, 2015. |   | May 11, 2015 |
|          |   |   |   |   |   |   |
| 10.104+       |   | 2006 Equity Incentive Plan - Form of Notice of Stock Option Grant. |   | Filed as Exhibit 10.104 to the Quarterly Report on Form 10‐Q for the quarter ended March 30, 2015. |   | May 11, 2015 |
|          |   |   |   |   |   |   |
| 10.105+       |   | Employment Agreement dated May 1, 2015 between the Registrant and Robert M. Vreeland. |   | Filed as Exhibit 10.105 to the Quarterly Report on Form 10‐Q for the quarter ended March 30, 2015. |   | May 11, 2015 |
|          |   |   |   |   |   |   |
| 10.106+       |   | Amended and Restated Employment Agreement dated December 31, 2015, between the Registrant and Andrew J. Littlefair. |   | Filed as Exhibit 10.106 to the Current Report on Form 8‐K. |   | December 31, 2015 |
|          |   |   |   |   |   |   |
| 10.107+       |   | Amended and Restated Employment Agreement dated December 31, 2015, between the Registrant and Robert M. Vreeland. |   | Filed as Exhibit 10.107 to the Current Report on Form 8‐K. |   | December 31, 2015 |
|          |   |   |   |   |   |   |
| 10.108+       |   | Amended and Restated Employment Agreement dated December 31, 2015, between the Registrant and Mitchell W. Pratt. |   | Filed as Exhibit 10.108 to the Current Report on Form 8‐K. |   | December 31, 2015 |
|          |   |   |   |   |   |   |

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|               |  |  |  |  |  |  |
| ExhibitNumber |   |   |   | Incorporated herein by reference to the following filings: |
|          | Description |   | Form |   | Filed on |
| 10.109+       |   | Amended and Restated Employment Agreement dated December 31, 2015, between the Registrant and Barclay F. Corbus. |   | Filed as Exhibit 10.109 to the Current Report on Form 8‐K. |   | December 31, 2015 |
|          |   |   |   |   |   |   |
| 10.110+       |   | Amended and Restated Employment Agreement dated December 31, 2015, between the Registrant and Peter J. Grace. |   | Filed as Exhibit 10.110 to the Current Report on Form 8‐K. |   | December 31, 2015 |
|          |   |   |   |   |   |   |
| 10.111        |   | Promissory Note dated February 29, 2016, between the Registrant, Clean Energy and PlainsCapital Bank. |   | Filed as Exhibit 10.111 to the Annual Report on Form 10-K for the year ended December 31, 2015. |   | March 3, 2016 |
|          |   |   |   |   |   |   |
| 10.112        |   | Pledged Account Agreement dated February 29, 2016, between Clean Energy, PlainsCapital Bank and PlainsCapital Bank - Wealth Management and Trust. |   | Filed as Exhibit 10.112 to the Annual Report on Form 10-K for the year ended December 31, 2015. |   | March 3, 2016 |
|          |   |   |   |   |   |   |
| 10.113        |   | Loan and Security Agreement dated February 29, 2016, between the Registrant, Clean Energy and PlainsCapital Bank. |   | Filed as Exhibit 10.113 to the Annual Report on Form 10-K for the year ended December 31, 2015. |   | March 3, 2016 |
|          |   |   |   |   |   |   |
| 10.114+       |   | Clean Energy Fuels Corp. 2016 Performance Incentive Plan. |   | Filed as Exhibit 10.114 to the Current Report on Form 8-K. |   | May 27, 2016 |
|          |   |   |   |   |   |   |
| 10.115        |   | Form of 7.5% Notes Exchange Agreement. |   | Filed as Exhibit 10.115 to the Current Report on Form 8-K. |   | July 15, 2016 |
|          |   |   |   |   |   |   |
| 10.116        |   | Form of 5.25% Notes Exchange Agreement. |   | Filed as Exhibit 10.116 to the Quarterly Report on Form 10-Q for the quarter ended June 30, 2016. |   | August 9, 2016 |
|          |   |   |   |   |   |   |
| 10.117+       |   | Clean Energy Fuels Corp. 2016 Performance Incentive Plan-Form of Notice of Stock Option Grant and Terms and Conditions of Nonqualified Stock Option. |   | Filed as Exhibit 10.117 to the Quarterly Report on Form 10-Q for the quarter ended June 30, 2016. |   | August 9, 2016 |
|          |   |   |   |   |   |   |
| 10.118+       |   | Clean Energy Fuels Corp. 2016 Performance Incentive Plan-Form of Notice of Stock Unit Award and Terms and Conditions of Stock Unit Award. |   | Filed as Exhibit 10.118 to the Quarterly Report on Form 10-Q for the quarter ended June 30, 2016. |   | August 9, 2016 |
|          |   |   |   |   |   |   |
| 10.119        |   | Loan Modification Agreement dated October 31, 2016, between the Registrant, Clean Energy and PlainsCapital Bank. |   | Filed as Exhibit 10.116 to the Quarterly Report on Form 10-Q for the quarter ended September 30, 2016. |   | November 3, 2016 |
|          |   |   |   |   |   |   |
| 10.120        |   | Note Repurchase Agreement dated February 6, 2017, by and between the Registrant and T. Boone Pickens. |   | Filed as Exhibit 10.119 to the Current Report on Form 8-K. |   | February 6, 2017 |
|          |   |   |   |   |   |   |
| 10.121+       |   | Form of Option Surrender Agreement. |   | Filed as Exhibit 10.120 to the Quarterly Report on Form 10-Q for the quarter ended March 31, 2017. |   | May 4, 2017 |
|          |   |   |   |   |   |   |
| 10.122        |   | Contribution Agreement dated July 14, 2017, by and between Clean Energy and NG Advantage LLC. |   | Filed as Exhibit 10.121 to the Quarterly Report on Form 10-Q for the quarter ended September 30, 2017. |   | November 2, 2017 |
|          |   |   |   |   |   |   |
| 10.123        |   | Series A Preferred Units Issuance Agreement dated July 14, 2017, by and between Clean Energy and NG Advantage LLC. |   | Filed as Exhibit 10.122 to the Quarterly Report on Form 10-Q for the quarter ended September 30, 2017. |   | November 2, 2017 |
|          |   |   |   |   |   |   |

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|               |  |  |  |  |  |  |
| ExhibitNumber |   |   |   | Incorporated herein by reference to the following filings: |
|          | Description |   | Form |   | Filed on |
| 10.124+       |   | Retirement Agreement dated September 15, 2017, by and between the registrant and Peter J. Grace. |   | Filed as Exhibit 10.123 to the Quarterly Report on Form 10-Q for the quarter ended September 30, 2017. |   | November 2, 2017 |
|          |   |   |   |   |   |   |
| 21.1**        |   | Subsidiaries. |   |   |   |   |
|          |   |   |   |   |   |   |
| 23.1**        |   | Consent of Independent Registered Public Accounting Firm KPMG LLP. |   |   |   |   |
|          |   |   |   |   |   |   |
| 24.1**        |   | Power of Attorney (included on the signature to the Original Annual Report). |   |   |   |   |
|          |   |   |   |   |   |   |
| 31.1**        |   | Certification of Andrew J. Littlefair, President and Chief Executive Officer, pursuant to Rule 13a-14(a) or 15d-14(a) of the Securities and Exchange Act of 1934, as adopted pursuant to Section 302 of the Sarbanes- Oxley Act of 2002. |   |   |   |   |
|          |   |   |   |   |   |   |
| 31.2**        |   | Certification of Robert M. Vreeland, Chief Financial Officer, pursuant to Rule 13a-14(a) or 15d-14(a) of the Securities and Exchange Act of 1934, as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002. |   |   |   |   |
|          |   |   |   |   |   |   |
| 31.3*         |   | Certification of Andrew J. Littlefair, President and Chief Executive Officer, pursuant to Rule 13a-14(a) or 15d-14(a) of the Securities and Exchange Act of 1934, as adopted pursuant to Section 302 of the Sarbanes- Oxley Act of 2002. |   |   |   |   |
|          |   |   |   |   |   |   |
| 31.4*         |   | Certification of Robert M. Vreeland, Chief Financial Officer, pursuant to Rule 13a-14(a) or 15d-14(a) of the Securities and Exchange Act of 1934, as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002. |   |   |   |   |
|          |   |   |   |   |   |   |
| 32.1**        |   | Certification pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, executed by Andrew J. Littlefair, President and Chief Executive Officer, and Robert M. Vreeland Chief Financial Officer. |   |   |   |   |
|          |   |   |   |   |   |   |
| 99.1          |   | Natural Gas Hedge Policy dated May 29, 2008. |   | Filed as Exhibit 99.1 to the Current Report on Form 8-K. |   | June 20, 2008 |
|          |   |   |   |   |   |   |
| 101**         |   | The following materials from the Company's Annual Report on Form 10-K for the year ended December 31, 2017, formatted in XBRL (eXtensible Business Reporting Language): |   |   |   |   |
|          |   | (i) Consolidated Balance Sheets; |   |   |   |   |
|          |   |   |   |   |   |   |
|          |   | (ii) Consolidated Statements of Operations; |   |   |   |   |
|          |   |   |   |   |   |   |
|          |   | (iii) Consolidated Statements of Comprehensive Income (Loss); |   |   |   |   |
|          |   |   |   |   |   |   |
|          |   | (iv) Consolidated Statements of Stockholders' Equity; |   |   |   |   |
|          |   |   |   |   |   |   |
|          |   | (v) Consolidated Statements of Cash Flows; and |   |   |   |   |
|          |   |   |   |   |   |   |
|          |   | (vi) Notes to Consolidated Financial Statements. |   |   |   |   |

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| § | Schedules and exhibits omitted pursuant to Item 601(b)(2) of Regulation S-K promulgated by the SEC. The registrant agrees to furnish a supplemental copy of any omitted schedules or exhibits to the SEC upon request. |

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| † | Portions of this exhibit have been omitted pursuant to the grant of a request for confidential treatment and the non-public information has been filed separately with the SEC. |

|   |                 |
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| * | Filed herewith. |

|    |                                                                                                           |
|----|-----------------------------------------------------------------------------------------------------------|
| ** | Previously filed or furnished, as applicable, as the same-numbered exhibit to the Original Annual Report. |

|   |                                                          |
|---|----------------------------------------------------------|
| + | Management contract or compensatory plan or arrangement. |

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|        |  |  |  |  |  |
|   |   | CLEAN ENERGY FUELS CORP. |   |
|   |   | By: |   | /s/ ANDREW J. LITTLEFAIR |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   | Andrew J. Littlefair President and Chief Executive Officer |   |