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  Quarterly  Report  of  KeySpan  Corporation  (the
"Corporation")  on Form 10-Q for the period  ended  March 31, 2003 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: May 1, 2003