Nicor Gas Company
                                                                     Form 10-K/A
                                                                    Exhibit 31.1

                                  CERTIFICATION

I, Russ M. Strobel, President and Chief Executive Officer of Nicor Gas Company,
certify that:

1) I have reviewed this annual report on Form 10-K/A of Nicor Gas Company;

2) Based on my knowledge, this report does not contain any untrue statement
   of a material fact or omit to state a material fact necessary to make the
   statements made, in light of the circumstances under which such statements
   were made, not misleading with respect to the period covered by this report;

3) Based on my knowledge, the financial statements, and other financial
   information included in this report, fairly present in all material
   respects the financial condition, results of operations and cash flows of
   the registrant as of, and for, the periods presented in this report;

4) The registrant's other certifying officer(s) and I are responsible for
   establishing and maintaining disclosure controls and procedures (as
   defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant
   and have:

   a) Designed such disclosure controls and procedures, or caused such
      disclosure controls and procedures to be designed under our supervision,
      to ensure that material information relating to the registrant, including
      its consolidated subsidiaries, is made known to us by others within those
      entities, particularly during the period in which this report is being
      prepared;

   b) Evaluated the effectiveness of the registrant's disclosure controls and
      procedures and presented in this report our conclusions about the
      effectiveness of the disclosure controls and procedures, as of the end of
      the period covered by this report based on such evaluation; and

   c) Disclosed in this report any change in the registrant's internal control
      over financial reporting that occurred during the registrant's most recent
      fiscal quarter (the registrant's fourth fiscal quarter in the case of an
      annual report) that has materially affected, or is reasonably likely to
      materially affect, the registrant's internal control over financial
      reporting; and

5) The registrant's other certifying officer(s) and I have disclosed, based
   on our most recent evaluation of internal control over financial
   reporting, to the registrant's auditors and the audit committee of the
   registrant's board of directors (or persons performing the equivalent
   functions):

   a) All significant deficiencies and material weaknesses in the design or
      operation of internal control over financial reporting which are
      reasonably likely to adversely affect the registrant's ability to
      record, process, summarize and report financial information; and

   b) Any fraud, whether or not material, that involves management or other
      employees who have a significant role in the registrant's internal
      control over financial reporting.


      Date    March 1, 2004                            /s/ RUSS M. STROBEL
            -----------------                          -------------------
                                                       Russ M. Strobel
                                                       President and
                                                       Chief Executive Officer