Nicor Gas Company
                                                                       Form 10-K
                                                                    Exhibit 31.1

                                  CERTIFICATION

I, Russ M. Strobel, certify that:

1) I have reviewed this annual report on Form 10-K 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)) and internal
control over financial reporting (as defined in Exchange Act Rules
13a-15(f) and 15d-15(f)) 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) Designed such internal control over financial reporting, or caused such
   internal control over financial reporting to be designed under our
   supervision, to provide reasonable assurance regarding the reliability of
   financial reporting and the preparation of financial statements for
   external purposes in accordance with generally accepted accounting
   principles;

   c) 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

   d) 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 February 28, 2005      /s/ RUSS M. STROBEL
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                               Russ M. Strobel
                               President and Chief Executive Officer