Document:

AMENDMENT NO. 9 TO ESCROW AGREEMENT

            THIS AMENDMENT NO. 9 to the Escrow Agreement is made as of the 11th
day of July, 2003 (as supplemented or modified from time to time, this
"Agreement") by and among AJG Financial Services, Inc., through its
Vice-President, General Counsel as agent (the "Major Shareholder Agent") for
Bernard J. Zahren, Finova Mezzanine Capital Corp., AJG Financial Services, Inc.,
Environmental Opportunities Fund (by itself and as successor to Environmental
Opportunities Fund Cayman), Fredric Rose, M&R Associates, Martin F. Laughlin,
Richard C. Augustine and Michael J. Carolan (each, an "Initial Major
Shareholder") and for Stephen Rosenberg, U.S. Energy Systems, Inc., a Delaware
corporation ("USE"), and US Energy Biogas Corp. (formerly known as Zahren
Alternative Power Corporation), as the successor to USE Acquisition Corp. a
Delaware corporation (the "Sub" and together with USE, the "USE Parties"),
Cinergy Energy Solutions, Inc., a Delaware corporation ("CES" and together with
the USE Parties, the "Beneficiaries"), and Tannenbaum Helpern Syracuse &
Hirschtritt LLP having an office at 900 Third Ave., New York, New York, 10022
(the "Escrow Agent"). Unless indicated otherwise, capitalized terms shall have
the same meanings herein as they have in the Escrow Agreement (as defined
below).

                              W I T N E S S E T H:

            WHEREAS, the parties hereto and the Initial Major Shareholders have
previously entered into that certain Escrow Agreement dated as of November 28,
2000 (as amended by Amendment No. 1 dated as of May 11, 2001, Amendment No. 2
dated as of November 1, 2002, Amendment No. 3 dated as of February 10, 2003,
Amendment No. 4 dated as of March 13, 2003, Amendment No. 5 dated as of April
15, 2003, Amendment No. 6 dated as of May 14, 2003, Amendment No. 7 dated as of
June 11, 2003 and Amendment No. 8 dated as of June 27, 2003, the "Escrow
Agreement");

            WHEREAS, the parties hereto now wish to amend the Escrow Agreement;

            NOW, THEREFORE, in consideration of $10.00 and other consideration,
the receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

            1.    The last sentence of Section 3(d) of the Escrow Agreement is
                  hereby amended by deleting the existing sentence in its
                  entirety and inserting in its place the following sentence:

                  The "Release Date" shall be July 31, 2003.

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<PAGE>

            2.    Except as amended hereby, the Escrow Agreement is hereby
                  ratified and confirmed and, as so amended, remains in full
                  force and effect on the date hereof.

                                       2
<PAGE>

            IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be executed as of the date first written above.

                                        MAJOR SHAREHOLDER AGENT:
                                        AJG FINANCIAL SERVICES, INC.

                                        By: ____________________________________
                                            Name:
                                            Title:

                                        CINERGY ENERGY SOLUTIONS, INC.:

                                        By: ____________________________________
                                            Name:
                                            Title:

                                        U.S. ENERGY SYSTEMS, INC.:

                                        By: ____________________________________
                                            Name:
                                            Title:

                                        US ENERGY BIOGAS CORP:

                                        By: ____________________________________
                                        Name:
                                        Title:

                                        ESCROW AGENT:

                                        TANNENBAUM HELPERN SYRACUSE &
                                        HIRSCHTRITT LLP

                                        By: ____________________________________
                                               A Member of the Firm

                                       3AMENDMENT NO. 10 TO ESCROW AGREEMENT

            THIS AMENDMENT NO. 10 to the Escrow Agreement is made as of the 28th
day of July, 2003 (as supplemented or modified from time to time, this
"Agreement") by and among AJG Financial Services, Inc., through its
Vice-President, General Counsel as agent (the "Major Shareholder Agent") for
Bernard J. Zahren, Finova Mezzanine Capital Corp., AJG Financial Services, Inc.,
Environmental Opportunities Fund (by itself and as successor to Environmental
Opportunities Fund Cayman), Fredric Rose, M&R Associates, Martin F. Laughlin,
Richard C. Augustine and Michael J. Carolan (each, an "Initial Major
Shareholder") and for Stephen Rosenberg, U.S. Energy Systems, Inc., a Delaware
corporation ("USE"), and US Energy Biogas Corp. (formerly known as Zahren
Alternative Power Corporation), as the successor to USE Acquisition Corp. a
Delaware corporation (the "Sub" and together with USE, the "USE Parties"),
Cinergy Energy Solutions, Inc., a Delaware corporation ("CES" and together with
the USE Parties, the "Beneficiaries"), and Tannenbaum Helpern Syracuse &
Hirschtritt LLP having an office at 900 Third Ave., New York, New York, 10022
(the "Escrow Agent"). Unless indicated otherwise, capitalized terms shall have
the same meanings herein as they have in the Escrow Agreement (as defined
below).

                              W I T N E S S E T H:

            WHEREAS, the parties hereto and the Initial Major Shareholders have
previously entered into that certain Escrow Agreement dated as of November 28,
2000 (as amended by Amendment No. 1 dated as of May 11, 2001, Amendment No. 2
dated as of November 1, 2002, Amendment No. 3 dated as of February 10, 2003,
Amendment No. 4 dated as of March 13, 2003, Amendment No. 5 dated as of April
15, 2003, Amendment No. 6 dated as of May 14, 2003, Amendment No. 7 dated as of
June 11, 2003, Amendment No. 8 dated as of June 27, 2003 and Amendment No. 9
dated as of July 11, 2003, the "Escrow Agreement");

            WHEREAS, the parties hereto now wish to amend the Escrow Agreement;

            NOW, THEREFORE, in consideration of $10.00 and other consideration,
the receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

            1.    The last sentence of Section 3(d) of the Escrow Agreement is
                  hereby amended by deleting the existing sentence in its
                  entirety and inserting in its place the following sentence:

                  The "Release Date" shall be August 15, 2003.

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<PAGE>

            2.    Except as amended hereby, the Escrow Agreement is hereby
                  ratified and confirmed and, as so amended, remains in full
                  force and effect on the date hereof.

                                       2
<PAGE>

            IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be executed as of the date first written above.

                                        MAJOR SHAREHOLDER AGENT:
                                        AJG FINANCIAL SERVICES, INC.

                                        By: ____________________________________
                                            Name:
                                            Title:

                                        CINERGY ENERGY SOLUTIONS, INC.:

                                        By: ____________________________________
                                            Name:
                                            Title:

                                        U.S. ENERGY SYSTEMS, INC.:

                                        By: ____________________________________
                                            Name:
                                            Title:

                                        US ENERGY BIOGAS CORP:

                                        By: ____________________________________
                                        Name:
                                        Title:

                                        ESCROW AGENT:

                                        TANNENBAUM HELPERN SYRACUSE &
                                        HIRSCHTRITT LLP

                                        By: ____________________________________
                                               A Member of the Firm

                                       3AMENDMENT NO. 5 TO INDEMNIFICATION AGREEMENT

            THIS AMENDMENT NO. 5 to the Indemnification Agreement is made as of
the 15th day of April, 2003 (as supplemented or modified from time to time, this
"Agreement") by and among AJG Financial Services, Inc., by its Vice President,
General Counsel, as agent (the "Major Shareholder Agent") for Bernard J. Zahren,
Finova Mezzanine Capital Corp., AJG Financial Services, Inc., ("AJG")
Environmental Opportunities Fund (for itself and as successor to) Environmental
Opportunities Fund Cayman, Fredric Rose, M&R Associates, Martin F. Laughlin,
Richard J. Augustine and Michael J. Carolan (each, an "Initial Major
Shareholder"), Stephen Rosenberg, US Energy Biogas Corp. (formerly known as
Zahren Alternative Power Corporation), a Delaware corporation ("ZAPCO "), U.S.
Energy Systems, Inc., a Delaware corporation ("USE"), and Cinergy Energy
Solutions, Inc., a Delaware corporation ("CES"). Unless indicated otherwise,
capitalized terms shall have the same meanings herein as they have in the
Indemnification Agreement (as defined below).

                              W I T N E S S E T H:

            WHEREAS, the parties hereto, the Initial Major Shareholders and USE
Acquisition Corp, which was merged into ZAPCO, have previously entered into that
certain Indemnification Agreement dated as of November 28, 2000 (as amended by
Amendment No. 1 dated as of May 11, 2001, Amendment No. 2 dated as of November
1, 2002, and Amendment No. 3 dated as of February 10, 2003 and Amendment No. 4
dated as of March 13, 2003, the "Indemnification Agreement");

            WHEREAS, the parties hereto now wish to amend the Indemnification
Agreement:

            NOW, THEREFORE, in consideration of $10.00 and other consideration,
the receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

            1.    Section 4(a)(i) of the Indemnification Agreement is hereby
                  amended by deleting the existing section in its entirety and
                  inserting in its place the following section:

                  i. unless a Notice of Claim (as defined herein) has been
            delivered to the Major Shareholders, on or prior to May 15, 2003
            provided that notwithstanding anything to the contrary in this
            Section 4(a)(i) Notices of Claim arising from or relating to
            breaches of Section 3.10, 3.17 and 3.20 of the Merger Agreement may
            be delivered prior to the sixth anniversary of the Closing Date;

            2.    Clause (i) in Section 4(a) of the Indemnification Agreement
                  following "The ZAPCO Indemnitees shall not be entitled to
                  recover under Section 3(b):" is hereby amended by deleting the
                  existing clause in its entirety and inserting in its place the
                  following clause:

<PAGE>

                  i. unless a Notice of Claim (as defined herein) has been
            delivered to the Beneficiaries, on or prior to May 15, 2003 except
            that Notices of Claim arising from or relating to the breaches of
            Sections 4.09, 4.15 and 4.18 of the Merger Agreement may be
            delivered prior to the sixth anniversary of the Closing Date;

            3.    Except as amended hereby, the Indemnification Agreement is
                  hereby ratified and confirmed and, as so amended, remains in
                  full force and effect on the date hereof.

            IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be Executed as of the date first written above.

                                        US ENERGY BIOGAS CORP:

                                        By: ____________________________________
                                            Name:
                                            Title:

                                        MAJOR SHAREHOLDER AGENT:
                                        AJG FINANCIAL SERVICES, INC.

                                        By: ____________________________________
                                            Name:
                                            Title:

                                        CINERGY ENERGY SOLUTIONS, INC.:

                                        By: ____________________________________
                                            Name:
                                            Title:

                                        U.S. ENERGY SYSTEMS, INC.:

                                        By: ____________________________________
                                            Name:
                                            Title:

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