EXHIBIT 3.131

                            CERTIFICATE OF FORMATION
                                       OF
                               KEYSTONE POWER 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 Keystone
Power 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 Michael J. Young, NRG Energy, Inc., 1221 Nicollet
Mall, Suite 700, Minneapolis, Minnesota 55403-2445.

         IN WITNESS WHEREOF, the undersigned has executed this Certificate of
Formation of Keystone Power LLC this 8th day of May, 2000.

                                                 /s/ Michael J. Young
                                                 -------------------------------
                                                 Michael J. Young
                                                 Authorized Person