Exhibit 99.1


                            CERTIFICATION PURSUANT TO
                              U.S.C. SECTION 1350,
                       AS ADOPTED PURSUANT TO SECTION 906
                        OF THE SARBANES-OXLEY ACT OF 2002

     In  connection  with  the  Annual  Report  of  KeySpan   Corporation   (the
"Corporation") on Form 10-K for the period ended December 31, 2002 as filed with
the Securities  and Exchange  Commission on the date hereof (the  "Report"),  I,
Robert B.  Catell,  Chairman  and Chief  Executive  Officer of the  Corporation,
certify,  pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906
of the Sarbanes-Oxley Act of 2002, that:

     (1) The Report fully  complies  with the  requirements  of Section 13(a) or
15(d) of the Securities Exchange Act of 1934, amended; and

     (2)  The  information  contained  in the  Report  fairly  presents,  in all
material  respects,  the  financial  condition  and results of operations of the
Corporation.


                                                /s/ Robert B. Catell
                                                --------------------
                                                Name: Robert B. Catell
                                                Title: Chairman and Chief
                                                       Executive Officer
                                                Date: March 6, 2003



Note: A signed  original of this written  statement  required by Section 906 has
been provided to KeySpan Corporation and will be retained by KeySpan Corporation
and  furnished  to the  Securities  and  Exchange  Commission  or its staff upon
request.