EXHIBIT 3.5

                            CERTIFICATE OF FORMATION
                                       OF
                            BIG CAJUN II UNIT 4 LLC

         The undersigned, being a natural person 18 years of age or older and
for the purpose of forming a limited liability company for general business
purposes under the Delaware Limited Liability Act, hereby adopts the following
Certificate of Formation:

         1.       Name: The name of the limited liability company is Big Cajun
II Unit 4 LLC.

         2.       Registered Office: The address of the registered office of the
limited liability company is Corporation Trust Center, 1209 Orange Street, in
the City of Wilmington, County of New Castle. The name of its registered agent
at such address is The Corporation Trust Company.

         3.       Organizer: The name and address of the sole organizer of the
limited liability company is Karin M. Wentz, NRG Energy, Inc., 901 Marquette
Avenue, Suite 2300, Minneapolis, Minnesota 55402.

         IN WITNESS WHEREOF, the undersigned has executed this Certificate of
Formation of Big Cajun II Unit 4 LLC this 13th day of September, 2001.

                                                        /s/ Karin M. Wentz
                                                        ------------------------
                                                        Karin M. Wentz
                                                        Authorized Person