UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                           Washington, D.C. 20549

                                 FORM 10-K/A
                               Amendment No. 1

 [X]   Annual Report Pursuant to Section 13 or 15(d) of the Securities Exchange
       Act of 1934

                  For the fiscal year ended December 31, 1999

                                     or

 [ ]  Transition Report Pursuant to Section 13 or 15(d) of the Securities
      Exchange Act of 1934
                                                             I.R.S.
                                                            Employer
  Commission      Registrant, State of Incorporation,    Identification
  File Number         Address and Telephone Number           Number
----------------  -------------------------------------  ---------------

    1-7297        Nicor Inc.                               36-2855175
                  (An Illinois Corporation)
                  1844 Ferry Road
                  Naperville, Illinois 60563-9600
                  (630) 305-9500

Securities registered pursuant to Section 12(b) of the Act:
                                                   Name of each exchange on
          Title of each class                         which  registered
    ------------------------------------------     ------------------------
    Common Stock, par value $2.50 per share,       New York Stock Exchange
    including Preference Stock purchase rights     Chicago Stock Exchange

Securities registered pursuant to Section 12(g) of the Act:  None

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 and (2) has been subject to such filing requirements for
the past 90 days. Yes [X] No [ ]

Indicate by check mark if disclosure of delinquent  filers  pursuant to Item 405
of Regulation  S-K 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. [ ]

As of  February  29,  2000,  46,707,099  common  shares  were  outstanding.  The
aggregate  market  value of  voting  securities  held by  non-affiliates  of the
registrant was approximately $1.4 billion.

                     DOCUMENTS INCORPORATED BY REFERENCE

Portions of the company's 2000 Annual Meeting Definitive Proxy Statement,  dated
March 8, 2000, are incorporated by reference into Part III.



<PAGE>






                           PURPOSE OF AMENDMENT




This  Amendment  contains  the  financial  statements  of the Nicor Gas  Savings
Investment  Plan,  the Nicor Gas Thrift Plan and the Birdsall,  Inc.  Retirement
Savings Plan and is being filed pursuant to the provisions of Rule 15d-21 of the
Securities  Exchange Act of 1934 in place of separate  annual reports  otherwise
required to be filed on Form 11-K for employee benefit plans.


<PAGE>



Nicor Inc.
-------------------------------------------------------------------------------

Signature

Pursuant  to the  requirements  of the  Securities  Exchange  Act of  1934,  the
registrant  has duly  caused  this  amendment  to be signed on its behalf by the
undersigned, thereunto duly authorized.

                                   Nicor Inc.


Date  June 23, 2000                By      KATHLEEN L. HALLORAN
     ----------------                -----------------------------------
                                           Kathleen L. Halloran
                                           Executive Vice President
                                           Finance and Administration
                                           and Secretary






Nicor Inc.                                                              Page 36
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PART IV

Item 14.  Exhibits, Financial Statement Schedules, and Reports on Form 8-K

(a)   1) Financial Statements:

         See Item 8,  Financial  Statements  and  Supplementary  Data, on page
         19 filed herewith, for a list of financial statements.

      2) Financial Statement Schedules:

         Schedule
         Number                                              Page
         --------                                            ----
               Report of Independent Public Accountants       20
           II  Valuation and Qualifying Accounts              37

         Schedules other than those listed are omitted because they are not
         applicable.

      3) Exhibits Filed:

         See Exhibit Index beginning on page 39 filed herewith.

(b)      The company  did not file a report on Form 8-K during the fourth
         quarter of 1999.




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Nicor Inc.                                                              Page 39
-------------------------------------------------------------------------------

Exhibit Index

Exhibit
Number                              Description of Document

3.01 * Articles of Incorporation of the company.  (File No. 2-55451,  Form S-14,
Nicor Inc., Exhibit 1-03 and Exhibit B of Amendment No. 1 thereto.)

3.02 * Amendment to Articles of Incorporation  of the company.  (Proxy Statement
dated April 20, 1979, Nicor Inc., Item 3 thereto.)

3.03 * Amendment to Articles of Incorporation of the company. (File No. 2-68777,
Form S-16, Nicor Inc., Exhibit 2-01.)

3.04 * Amendment to Articles of Incorporation of the company.  (File No. 1-7297,
Form 10-K for 1985, Nicor Inc., Exhibit 3-03.)

3.05 * Amendment to Articles of Incorporation  of the company.  (Proxy Statement
dated March 12, 1987, Nicor Inc., Exhibit A and Exhibit B thereto.)

3.06 * Amendment to Articles of Incorporation of the company.  (File No. 1-7297,
Form 10-K for 1992, Nicor Inc., Exhibit 3-06.)

3.07 * Amendments to Articles of Incorporation of the company.  (Proxy Statement
dated March 9, 1994, Nicor Inc., Exhibit A-1 and Exhibit B thereto.)

3.08 * Amendment to Articles of Incorporation  of the company.  (Proxy Statement
dated March 6, 1998, Nicor Inc., Item 2 thereto.)

3.09 * By-Laws of the company as amended by the company's  board of Directors on
May 3, 1995.  (File No. 1-7297,  Form 10-Q for March 1995,  Nicor Inc.,  Exhibit
3(ii).01.)

4.01 * Indenture of Commonwealth Edison Company to Continental Illinois National
Bank and Trust Company of Chicago,  Trustee,  dated as of January 1, 1954. (File
No. 1-7296, Form 10-K for 1995, Nicor Gas, Exhibit 4.01.)

4.02 * Indenture of Adoption of Nicor Gas to Continental  Illinois National Bank
and Trust Company of Chicago, Trustee, dated February 9, 1954. (File No. 1-7296,
Form 10-K for 1995, Nicor Gas, Exhibit 4.02.)

4.03 * Supplemental  Indenture,  dated June 1, 1963, of Nicor Gas to Continental
Illinois  National Bank and Trust Company of Chicago,  Trustee,  under Indenture
dated as of January 1, 1954.  (File No.  2-21490,  Form S-9, Nicor Gas,  Exhibit
2-8.)

4.04 *  Supplemental  Indenture,  dated May 1, 1966, of Nicor Gas to Continental
Illinois  National Bank and Trust Company of Chicago,  Trustee,  under Indenture
dated as of January 1, 1954.  (File No.  2-25292,  Form S-9, Nicor Gas,  Exhibit
2-4.)


<PAGE>


Nicor Inc.                                                              Page 40

Exhibit Index (continued)

Exhibit
Number                              Description of Document

4.05 * Supplemental  Indenture,  dated June 1, 1971, of Nicor Gas to Continental
Illinois  National Bank and Trust Company of Chicago,  Trustee,  under Indenture
dated as of January 1, 1954.  (File No.  2-44647,  Form S-7, Nicor Gas,  Exhibit
2-03.)

4.06 *  Supplemental  Indenture,  dated April 30, 1976,  between the company and
Continental Illinois National Bank and Trust Company of Chicago,  Trustee, under
Indenture dated as of January 1, 1954.  (File No. 2-56578,  Form S-9, Nicor Gas,
Exhibit 2-25.)

4.07 * Supplemental Indenture, dated April 30, 1976, of Nicor Gas to Continental
Illinois  National Bank and Trust Company of Chicago,  Trustee,  under Indenture
dated as of January 1, 1954.  (File No.  2-56578,  Form S-9, Nicor Gas,  Exhibit
2-21.)

4.08  *  Supplemental  Indenture,  dated  August  15,  1991,  of  Nicor  Gas  to
Continental Bank,  National  Association,  Trustee,  under Indenture dated as of
January 1, 1954. (File No. 1-7296,  Form 8-K for August 1991, Nicor Gas, Exhibit
4-01.)

4.09 * Supplemental  Indenture,  dated October 15, 1995, of Nicor Gas to Bank of
America  Illinois,  Trustee,  under Indenture dated as of January 1, 1954. (File
No. 1-7296, Form 10-Q for September 1995, Nicor Gas, Exhibit 4.01.)

4.10 * Supplemental Indenture,  dated May 10, 1996, of Nicor Gas to Harris Trust
and Savings Bank,  Trustee,  under Indenture dated as of January 1, 1954.  (File
No. 1-7296, Form 10-Q for June 1996, Nicor Gas, Exhibit 4.01.)

4.11 *  Supplemental  Indenture,  dated  August 1, 1996,  of Nicor Gas to Harris
Trust and Savings Bank,  Trustee,  under  Indenture dated as of January 1, 1954.
(File No. 1-7296, Form 10-Q for June 1996, Nicor Gas, Exhibit 4.02.)

4.12 * Supplemental Indenture,  dated June 1, 1997, of Nicor Gas to Harris Trust
and Savings Bank,  Trustee,  under Indenture dated as of January 1, 1954.  (File
No. 1-7296, Form 10-Q for June 1997, Nicor Gas, Exhibit 4.01.)

4.13 *  Shareholder  Rights  Agreement,  dated  September  9, 1997,  between the
company and Harris Trust and Savings Bank, as Rights  Agent.  (File No.  1-7297,
Form 8-K for September 1997, Nicor Inc., Exhibit 1.)

4.14 *  Supplemental  Indenture,  dated October 15, 1997, of Nicor Gas to Harris
Trust and Savings Bank,  Trustee,  under  Indenture dated as of January 1, 1954.
(File No. 1-7296, Form 10-Q for September 1997, Nicor Gas, Exhibit 4.01.)

4.15 * Supplemental  Indenture,  dated February 15, 1998, of Nicor Gas to Harris
Trust and Savings Bank,  Trustee,  under  Indenture dated as of January 1, 1954.
(File No. 1-7296, Form 10-K for 1997, Nicor Gas, Exhibit 4.19.)


<PAGE>


Nicor Inc.                                                              Page 41

Exhibit Index (continued)

Exhibit
Number                              Description of Document

4.16 * Supplemental Indenture,  dated June 1, 1998, of Nicor Gas to Harris Trust
and Savings Bank,  Trustee,  under Indenture dated as of January 1, 1954.  (File
No. 1-7296, Form 10-Q for June 1998, Nicor Gas, Exhibit 4.01.)

4.17 *  Supplemental  Indenture,  dated February 1, 1999, of Nicor Gas to Harris
Trust and Savings Bank,  Trustee,  under  Indenture dated as of January 1, 1954.
(File No. 1-7296, Form 10-K for 1998, Nicor Gas, Exhibit 4.19.)

Other debt instruments are omitted in accordance with Item  601(b)(4)(iii)(A) of
Regulation  S-K.  Copies of such  agreements will be furnished to the Commission
upon request.

10.01 * 1984 Nicor Officers' Capital Accumulation Plan Participation  Agreement.
(File No. 1-7297, Form 10-K for 1988, Nicor Inc., Exhibit 10-10.)

10.01(a)  *  1985  Nicor  Officers'  Capital   Accumulation  Plan  Participation
Agreement. (File No. 1-7297, Form 10-K for 1988, Nicor Inc., Exhibit 10-10(a).)

10.02 * 1984 Nicor Directors' Capital Accumulation Plan Participation Agreement.
(File No. 1-7297, Form 10-K for 1983, Nicor Inc., Exhibit 10-13.)

10.02(a)  *  1985  Nicor  Directors'  Capital  Accumulation  Plan  Participation
Agreement. (File No. 1-7297, Form 10-K for 1984, Nicor Inc., Exhibit 10-13(a).)

10.03 * Directors'  Deferred  Compensation Plan. (File No. 1-7297, Form 10-K for
1983, Nicor Inc., Exhibit 10-16.)

10.04 * Directors'  Pension Plan.  (File No. 1-7297,  Form 10-K for 1985,  Nicor
Inc., Exhibit 10-18.)

10.05 * Flexible  Spending Account for Executives.  (File No. 1-7297,  Form 10-K
for 1986, Nicor Inc., Exhibit 10-20.)

10.06 * Amendment and Restatement of the Nicor Gas Incentive  Compensation Plan.
(File No. 1-7297, Form 10-K for 1986, Nicor Inc., Exhibit 10-21.)

10.07 * Nicor Inc. 1989 Long-Term  Incentive Plan.  (Filed with Nicor Inc. Proxy
Statement, dated April 20, 1989, Exhibit A.)

10.08 * Nicor Gas Supplementary Retirement Plan. (File No. 1-7297, Form 10-K for
1989, Nicor Inc., Exhibit 10-24.)

10.09 * Nicor Gas  Supplementary  Savings Plan. (File No. 1-7297,  Form 10-K for
1989, Nicor Inc., Exhibit 10-25.)



<PAGE>


Nicor Inc.                                                              Page 42

Exhibit Index (continued)

Exhibit
Number                              Description of Document

10.10 * Nicor Salary Deferral Plan. (File No. 1-7297,  Form 10-K for 1989, Nicor
Inc., Exhibit 10-29.)

10.11 * Nicor  Inc.  Stock  Deferral  Plan.  (File  No.  1-7297,  Form  10-Q for
September 1996, Nicor Inc., Exhibit 10.01.)

10.12 * Amendment to Nicor Inc. Stock Deferral Plan. (File No. 1-7297, Form 10-K
for 1997, Nicor Inc., Exhibit 10.22.)

10.13 * Nicor Inc. 1995 Directors' Stock Plan.  (File No. 1-7297,  Form 10-Q for
September 1996, Nicor Inc., Exhibit 10.02.)

10.14 * 1995 Long-Term Incentive Program.  (File No. 1-7297, Form 10-K for 1994,
Nicor Inc., Exhibit 10.17.)

10.15 * 1997 Long-Term Incentive Program.  (File No. 1-7297, Form 10-Q for March
1997, Nicor Inc., Exhibit 10.01.)

10.16 * Nicor Inc. 1997 Long-Term  Incentive Plan.  (Filed as an appendix to the
Nicor Inc. Proxy Statement, dated March 6, 1997.)

10.17 * 1998 Long-Term Incentive Program.  (File No. 1-7297, Form 10-K for 1997,
Nicor Inc., Exhibit 10.25.)

10.18 * 1999 Nicor Incentive  Compensation Plan. (File No. 1-7297, Form 10-K for
1998, Nicor Inc., Exhibit 10.24.)

10.19 * 1999 Nicor Gas Incentive  Compensation Plan. (File No. 1-7297, Form 10-K
for 1998, Nicor Inc., Exhibit 10.25.)

10.20 * 1999 Long-Term Incentive Program.  (File No. 1-7297, Form 10-K for 1998,
Nicor Inc. Exhibit 10.26.)

10.21 2000 Nicor Incentive Compensation Plan.

10.22 2000 Nicor Gas Incentive Compensation Plan.

10.23 2000 Long-Term Incentive Program.

10.24 Security Payment Plan.

10.25 Letter Agreement,  executed January 19, 2000,  between Mr. Nardi and Nicor
Inc.


<PAGE>


Nicor Inc.                                                              Page 43

Exhibit Index (concluded)

Exhibit
Number                              Description of Document

10.26 Resolutions adopted by the Board of Directors on December 7, 1999 amending
the Nicor Inc.  Stock  Deferral  Plan and amending the  definition  of change in
control in the Long- Term Incentive  Plan,  Salary Deferral Plan and the Capital
Accumulation Plan.

10.27  Summary of proposed  change in control  agreements  between Nicor and Mr.
Fisher,  Mr.  Cali and Ms.  Halloran  (incorporated  by  reference  to the third
paragraph under "Change in Control  Arrangements"  of Nicor Inc. Proxy Statement
dated March 8, 2000, Nicor Inc., File No. 1-7297.)


Exhibits 10.01 through 10.27  constitute  management  contracts and compensatory
plans and arrangements required to be filed as exhibits to this Form pursuant to
Item 14(c) of Form 10-K.

21.01 * Subsidiaries.  (File No. 69-228,  Form U-3A-2 for 1999, Nicor Inc., Item
1.)

23.01 Consent of Independent Public Accountants.

23.02 Consent of Independent  Public  Accountants--Nicor  Gas Savings Investment
Plan, Nicor Gas Thrift Plan and Birdsall, Inc. Retirement Savings Plan.

24.01 Powers of Attorney.

27.01 Financial Data Schedule.

99.01 * Form of Letter to Shareholders relating to Shareholder Rights Agreement.
(File No. 1-7297, Form 8-K for September 1997, Nicor Inc., Exhibit 2.)

99.02 Financial Statements of the Nicor Gas Savings Investment Plan for 1999.

99.03 Financial Statements of the Nicor Gas Thrift Plan for 1999.

99.04 Financial  Statements of the Birdsall,  Inc.  Retirement  Savings Plan for
1999.



* These  exhibits have been  previously  filed with the  Securities and Exchange
Commission as exhibits to  registration  statements or to other filings with the
Commission and are incorporated herein as exhibits by reference. The file number
and exhibit  number of each such  exhibit,  where  applicable,  are  stated,  in
parentheses, in the description of such exhibit.

Upon  written  request,  the company  will  furnish free of charge a copy of any
exhibit.  Requests  should  be  sent  to  Investor  Relations  at the  corporate
headquarters.