Document:

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                                                                   EXHIBIT 10.22

                        CONSOLIDATED TERM PROMISSORY NOTE

$2,146,660.93                                                     April 3, 2002

         FOR VALUE RECEIVED, in the manner, on the dates and in the amounts
herein stipulated, NATURAL GAS SERVICES GROUP, INC., a Colorado corporation
("Borrower"), hereby promises and agrees to pay to the order of WESTERN NATIONAL
BANK, a national banking association ("Lender"), in Midland, Midland County,
Texas, the principal sum of Two Million One Hundred Forty Six Thousand Six
Hundred Sixty and 93/100 Dollars ($2,146,660.93) in lawful money of the United
States of America, which shall be legal tender in payment of all debts and dues,
public and private, at the time of payment, together with interest on the unpaid
principal amount hereof from time to time outstanding until maturity at a rate
per annum which shall from day to day be equal to the lesser of (a) one percent
(1.00%) over the Prime Rate (the "Established Rate") in effect from day to day
(calculated on the basis of actual days elapsed, but computed as if each
calendar year consisted of 360 days) or (b) the Highest Lawful Rate. Each change
in the rate of interest charged under this Consolidated Term Promissory Note
(this "Note") shall, subject to the terms hereof, become effective, without
notice to Borrower, upon the effective date of each change in the Prime Rate or
the Highest Lawful Rate, as the case may be. Notwithstanding the foregoing, if
at any time the Established Rate exceeds the Highest Lawful Rate, the rate of
interest on this Note shall be limited to the Highest Lawful Rate, but any
subsequent reductions in the Established Rate shall not reduce the rate of
interest hereon below the Highest Lawful Rate until the total amount of interest
accrued hereon approximately equals the amount of interest which would have
accrued hereon if the Established Rate had at all times been in effect. In the
event that at maturity (stated or by acceleration), or at final payment of this
Note, the total amount of interest paid or accrued hereon is less than the
amount of interest which would have accrued if the Established Rate had at all
times been in effect, then, at such time and to the extent permitted by
applicable laws, Borrower shall pay to Lender an amount equal to the difference
between (a) the lesser of the amount of interest which would

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have accrued if the Established Rate had at all times been in effect or the
amount of interest which would have accrued if the Highest Lawful Rate had at
all times been in effect, and (b) the amount of interest actually paid or
accrued on this Note. Interest calculations may be made ten days prior to any
interest install ment due date under this Note, in which event, if there is an
adjustment in the interest rate in accordance with the terms hereof during such
ten- day period, then Borrower shall subsequently, on demand, pay to Lender any
underpayment, or Lender shall pay to Borrower, any overpayment, as the case may
be, as a result of any adjustment during such ten-day period.

         This Note is given in renewal, rearrangement and consolidation, but not
extinguishment or novation, of the Term A Promissory Note, Term B Promissory
Note and the Term C Promissory Note, and is the Consolidated Term Promissory
Note referred to in the Loan Agreement, dated as of September 15, 1999, as
amended by that certain First Amendment and Waiver to Loan Agreement, dated as
of March 9, 2001, as further amended by that certain Second Amendment to Loan
Agreement, dated as of March 20, 2001, as further amended by that certain Third
Amendment and Waiver to Loan Agreement, dated as of July 25, 2001, as further
amended by that certain Fourth Amendment to Loan Agreement, dated as of December
12, 2001, and as further amended by that certain Fifth Amendment to Loan
Agreement, dated as of April 3, 2002 (said Loan Agreement, as amended, and as
the same may be further amended, supplemented or otherwise modified from time to
time, the "Loan Agreement"), by and between Borrower and Lender, and is subject
to the terms and conditions thereof. Reference is made to the Loan Agreement for
provisions for the disbursement of funds hereunder and for a further statement
of the rights, remedies, powers, privileges, benefits, duties and obligations of
Borrower and Lender under the Loan Agreement and this Note. Terms used herein
which are defined in the Loan Agreement shall have such defined meanings unless
otherwise defined herein. The holder of this Note shall be entitled to the
benefits of the Loan Agreement.

         The principal of this Note shall be due and payable (a) in forty- seven
consecutive monthly installments of $45,746.00 each, with the first such
installment being due and payable on April 15, 2002, and a like installment
being due and payable on the fifteenth day of each succeeding month to and
including February 15, 2006; and (b) one final installment

                                      -2-

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in an amount equal to all remaining unpaid principal and accrued and unpaid
interest on this Note shall be due and payable on March 15, 2006. Interest,
computed on the unpaid balance of this Note, shall be due and payable as it
accrues, on the same dates as, but in addition to, the installments of
principal. All payments and prepayments shall be applied first to accrued and
unpaid interest, and the balance to principal. Partial prepayments of principal
shall be applied to the installments of principal thereof in the inverse order
of their maturity. All of the past due principal and accrued interest hereunder
shall, at the option of Lender, bear interest from maturity (stated or by
acceleration) until paid at a rate per annum equal to the Highest Lawful Rate.

         This Note is secured as provided in the Loan Agreement and in the other
Loan Papers, to which reference is hereby made for a description of the
properties and assets in which a lien and security interest has been granted,
the nature and extent of the security, the terms and conditions upon which the
liens and security interests were granted and the rights of the holder of this
Note with respect thereto.

         Time is of the essence of this Note. Upon the occurrence of any one or
more of the Events of Default specified in the Loan Agreement, all amounts then
remaining unpaid on this Note shall become, or may be declared to be,
immediately due and payable, all as provided therein.

         Borrower and any and all co-makers, endorsers, guarantors and sureties
severally waive notice (including, but not limited to, notice of protest, notice
of dishonor, notice of intent to accelerate and notice of acceleration), demand,
presentment for payment, protest, diligence in collecting or bringing suit and
the filing of suit for the purpose of fixing liability, and consent that the
time of payment hereof may be extended and re-extended from time to time without
notice to them or any of them, and each agrees that his, her or its liability on
or with respect to this Note shall not be affected, diminished or impaired by
any (a) release of any security at any time existing for this Note, (b)
substitution for any security at any time existing for this Note, or (c) failure
to perfect (or to maintain perfection of) any lien on or security interest in
any such security, in each case in whole or in part, with or without notice,
before or after maturity.

                                      -3-

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         It is the intention of Borrower and Lender that Lender shall conform
strictly to usury laws applicable to it. Accordingly, if the transactions
contemplated by the Loan Agreement and this Note would be usurious as to Lender
under laws applicable to it (including the laws of the United States of America
and the State of Texas or any other jurisdiction whose laws may be mandatorily
applicable to Lender notwithstanding the other provisions of the Loan Agreement
and this Note), then, in that event, notwithstanding anything to the contrary in
this Note, the Loan Agreement or any other Loan Paper or other agreement entered
into in connection with or as security for this Note, (i) the aggregate of all
consideration which is contracted for, taken, reserved, charged or received by
Lender under this Note, the Loan Agreement or any other Loan Paper or agreement
entered into in connection with or as security for this Note shall under no
circumstances exceed the maximum amount allowed by such applicable law, and any
excess shall be credited by Lender on the principal amount of the Obligations to
Lender (or, to the extent that the principal amount of the Obligations shall
have been or would thereby be paid in full, refunded by Lender to the Borrower);
and (ii) in the event that the maturity of this Note is accelerated by reason of
an Event of Default under the Loan Agreement or otherwise, or in the event of
any prepayment, then such consideration that constitutes interest under law
applicable to Lender may never include more than the maximum amount allowed by
such applicable law, and excess interest, if any, provided for in this Note, the
Loan Agreement or otherwise shall be cancelled automatically by Lender as of the
date of such acceleration of prepayment and, if theretofore paid, shall be
credited by Lender on the principal amount of the Obligations (or, to the extent
that the principal amount of such Obligations shall have been or would thereby
be paid in full, refunded by Lender to the Borrower).

         To the extent that Texas Finance Code Section 303.002 is relevant to
Lender for the purposes of determining the Highest Lawful Rate, the applicable
rate ceiling under such provisions shall be determined by the indicated (weekly)
rate ceiling from time to time in effect, subject to Lender's right subsequently
to change such method in accordance with applicable law. Notwithstanding
anything to the contrary contained herein or in any of the other Loan Papers, it
is not the intention of the Lender to accelerate the maturity of any interest
that has not accrued at the time of such acceleration or to collect unearned
interest at the time of such acceleration.

                                      -4-

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         This Note is performable and payable in the County of Midland, State of
Texas, and shall be construed in accordance with, and governed by, the laws of
the State of Texas; provided, however, that the laws pertaining to allowable
rates of interest may, from time to time, be governed by the laws of the United
States of America.

                                      NATURAL GAS SERVICES GROUP, INC.

                                      By: /s/ Wayne Vinson
                                          -------------------------------------
                                          Wayne Vinson, President

                                      -5-<PAGE>
                                                                   EXHIBIT 10.23

                    REVOLVING LINE OF CREDIT PROMISSORY NOTE

$750,000.00                                                       April 3, 2002

         FOR VALUE RECEIVED, in the manner, on the dates and in the amounts
herein stipulated, NATURAL GAS SERVICES GROUP, INC., a Colorado corporation
("Borrower"), hereby promises and agrees to pay to the order of WESTERN NATIONAL
BANK, a national banking association ("Lender"), in Midland, Midland County,
Texas, the principal sum of Seven Hundred Fifty Thousand and No/100 Dollars
($750,000.00) or, if less, the aggregate unpaid principal amount outstanding
hereunder, in lawful money of the United States of America, which shall be legal
tender in payment of all debts and dues, public and private, at the time of
payment, together with interest on the unpaid principal amount hereof from time
to time outstanding until maturity at a rate per annum which shall from day to
day be equal to the lesser of (a) one percent (1.00%) over the Prime Rate (the
"Established Rate") in effect from day to day (calculated on the basis of actual
days elapsed, but computed as if each calendar year consisted of 360 days) or
(b) the Highest Lawful Rate. Each change in the rate of interest charged under
this Revolving Line of Credit Promissory Note (this "Note") shall, subject to
the terms hereof, become effective, without notice to Borrower, upon the
effective date of each change in the Prime Rate or the Highest Lawful Rate, as
the case may be. Notwithstanding the foregoing, if at any time the Established
Rate exceeds the Highest Lawful Rate, the rate of interest on this Note shall be
limited to the Highest Lawful Rate, but any subsequent reductions in the
Established Rate shall not reduce the rate of interest hereon below the Highest
Lawful Rate until the total amount of interest accrued hereon approximately
equals the amount of interest which would have accrued hereon if the Established
Rate had at all times been in effect. In the event that at maturity (stated or
by acceleration), or at final payment of this Note, the total amount of interest
paid or accrued hereon is less than the amount of interest which would have
accrued if the Established Rate had at all times been in effect, then, at such
time and to the extent permitted by applicable laws, Borrower shall pay to
Lender an amount equal to the difference between (a) the lesser of the amount of
interest which would have accrued if the Established Rate

<PAGE>

had at all times been in effect or the amount of interest which would have
accrued if the Highest Lawful Rate had at all times been in effect, and (b) the
amount of interest actually paid or accrued on this Note. Interest calculations
may be made ten days prior to any interest installment due date under this Note,
in which event, if there is an adjustment in the interest rate in accordance
with the terms hereof during such ten-day period, then Borrower shall
subsequently, on demand, pay to Lender any underpayment, or Lender shall pay to
Borrower, any overpayment, as the case may be, as a result of any adjustment
during such ten-day period.

         This Note (i) is given in renewal, extension and rearrangement, but not
in extinguishment, of that certain Revolving Line of Credit Promissory Note,
dated December 12, 2001, in the original principal amount of $750,000.00, and
(ii) is the Revolving Line of Credit Promissory Note referred to in the Loan
Agreement, dated as of September 15, 1999, as amended by that certain First
Amendment and Waiver to Loan Agreement, dated as of March 9, 2001, as further
amended by that certain Second Amendment to Loan Agreement, dated as of March
20, 2001, as further amended by that certain Third Amendment and Waiver to Loan
Agreement, dated as of July 25, 2001, as further amended by that certain Fourth
Amendment to Loan Agreement, dated as of December 12, 2001, and as further
amended by that certain Fifth Amendment to Loan Agreement, dated as of April 3,
2002 (said Loan Agreement, as amended, and as the same may be further amended,
supplemented or otherwise modified from time to time, the "Loan Agreement"), by
and between Borrower and Lender, and is subject to the terms and conditions
thereof. Reference is made to the Loan Agreement for provisions for the
disbursement of funds hereunder and for a further statement of the rights,
remedies, powers, privileges, benefits, duties and obligations of Borrower and
Lender under the Loan Agreement and this Note. Terms used herein which are
defined in the Loan Agreement shall have such defined meanings unless otherwise
defined herein. The holder of this Note shall be entitled to the benefits of the
Loan Agreement.

         Advances and Subsequent Advances under this Note shall be made in
accordance with the provisions of the Loan Agreement. Subject to the terms
hereof and of the Loan Agreement, Borrower may borrow, repay and reborrow at any
time and from time to time under this Note; provided, however, that the
principal sum outstanding hereunder at any one time shall never exceed the
lesser of (i) $750,000.00 or (ii) the Borrowing Base then in effect.

                                       -2-

<PAGE>

         Interest on the outstanding principal balance of this Note shall be due
and payable on the fifteenth day of each month, commencing April 15, 2002. The
then outstanding principal balance of this Note and all accrued and unpaid
interest shall be due and payable on March 15, 2003. All of the past due
principal and accrued interest hereunder shall, at the option of Lender, bear
interest from maturity (stated or by acceleration) until paid at a rate per
annum equal to the Highest Lawful Rate.

         This Note is secured as provided in the Loan Agreement and in the other
Loan Papers, to which reference is hereby made for a description of the
properties and assets in which a lien and security interest has been granted,
the nature and extent of the security, the terms and conditions upon which the
liens and security interests were granted and the rights of the holder of this
Note with respect thereto.

         Time is of the essence of this Note. Upon the occurrence of any one or
more of the Events of Default specified in the Loan Agreement, all amounts then
remaining unpaid on this Note shall become, or may be declared to be,
immediately due and payable, all as provided therein.

         Borrower and any and all co-makers, endorsers, guarantors and sureties
severally waive notice (including, but not limited to, notice of protest, notice
of dishonor, notice of intent to accelerate and notice of acceleration), demand,
presentment for payment, protest, diligence in collecting or bringing suit and
the filing of suit for the purpose of fixing liability, and consent that the
time of payment hereof may be extended and re-extended from time to time without
notice to them or any of them, and each agrees that his, her or its liability on
or with respect to this Note shall not be affected, diminished or impaired by
any (a) release of any security at any time existing for this Note, (b)
substitution for any security at any time existing for this Note, or (c) failure
to perfect (or to maintain perfection of) any lien on or security interest in
any such security, in each case in whole or in part, with or without notice,
before or after maturity.

         It is the intention of Borrower and Lender that Lender shall conform
strictly to usury laws applicable to it. Accordingly, if the transactions
contemplated by the Loan Agreement and this Note would be usurious as to Lender
under laws applicable to it (including the laws of the United States of America
and the State of Texas or any other jurisdiction whose laws may be mandatorily
applicable to Lender notwithstanding the other provisions of the Loan Agreement
and this Note), then, in that event,

                                       -3-

<PAGE>

notwithstanding anything to the contrary in this Note, the Loan Agreement or any
other Loan Paper or other agreement entered into in connection with or as
security for this Note, (i) the aggregate of all consideration which is
contracted for, taken, reserved, charged or received by Lender under this Note,
the Loan Agreement or any other Loan Paper or agreement entered into in
connection with or as security for this Note shall under no circumstances exceed
the maximum amount allowed by such applicable law, and any excess shall be
credited by Lender on the principal amount of the Obligations to Lender (or, to
the extent that the principal amount of the Obligations shall have been or would
thereby be paid in full, refunded by Lender to the Borrower); and (ii) in the
event that the maturity of this Note is accelerated by reason of an Event of
Default under the Loan Agreement or otherwise, or in the event of any
prepayment, then such consideration that constitutes interest under law
applicable to Lender may never include more than the maximum amount allowed by
such applicable law, and excess interest, if any, provided for in this Note, the
Loan Agreement or otherwise shall be cancelled automatically by Lender as of the
date of such acceleration of prepayment and, if theretofore paid, shall be
credited by Lender on the principal amount of the Obligations (or, to the extent
that the principal amount of such Obligations shall have been or would thereby
be paid in full, refunded by Lender to the Borrower).

         To the extent that Texas Finance Code Section 303.002 is relevant to
Lender for the purposes of determining the Highest Lawful Rate, the applicable
rate ceiling under such provisions shall be determined by the indicated (weekly)
rate ceiling from time to time in effect, subject to Lender's right subsequently
to change such method in accordance with applicable law. Notwithstanding
anything to the contrary contained herein or in any of the other Loan Papers, it
is not the intention of the Lender to accelerate the maturity of any interest
that has not accrued at the time of such acceleration or to collect unearned
interest at the time of such acceleration.

                                       -4-

<PAGE>

         This Note is performable and payable in the County of Midland, State of
Texas, and shall be construed in accordance with, and governed by, the laws of
the State of Texas; provided, however, that the laws pertaining to allowable
rates of interest may, from time to time, be governed by the laws of the United
States of America.

                                               NATURAL GAS SERVICES GROUP, INC.

                                               By:  /s/ Wayne Vinson
                                                  -----------------------------
                                                    Wayne Vinson, President

                                      -5-

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