<PAGE>   1
                                                                    Exhibit 10.2



                              GAS PURCHASE CONTRACT

                   BETWEEN RANGE PRODUCTION I, L.P. AS SELLER

                            AND CONOCO INC. AS BUYER

                               DATED JULY 1, 2000


                                       58
<PAGE>   2
                              GAS PURCHASE CONTRACT
                   BETWEEN RANGE PRODUCTION I, L.P. AS SELLER
                            AND CONOCO INC. AS BUYER
                               DATED JULY 1, 2000.
                                      INDEX

<TABLE>
<CAPTION>
PARAGRAPH
---------
<S>                                                                         <C>
1.     COMMITMENT ........................................................     1

2.     POINTS OF DELIVERY ................................................     1

3.     DELIVERY PRESSURE AND QUANTITY ....................................     1

4.     PRICE .............................................................     2

5.     TERM ..............................................................     5

6.     ADDRESSES AND NOTICES .............................................     5

7.     UNPROFITABILITY ...................................................     6


                     EXHIBIT A GENERAL TERMS AND CONDITIONS

A.     DEFINITIONS .......................................................     8

B      DELIVERY DATE .....................................................    10

C.     RESERVATIONS OF SELLER ............................................    11

D.     METERING ..........................................................    12

E.     DETERMINATION OF GAS COMPOSITION ..................................    14

F.     QUALITY OF GAS ....................................................    14

G.     BILLING AND PAYMENT ...............................................    15

H.     FORCE MAJEURE .....................................................    16

I.     TITLE, OWNERSHIP ..................................................    17

J.     ROYALTY ...........................................................    17

K.     SEVERANCE AND SIMILAR TAXES .......................................    17

L.     LAWS AND REGULATIONS ..............................................    17

M.     RIGHT OF WAY AND INGRESS, EGRESS ..................................    18

N.     ASSIGNMENT ........................................................    18

O.     MISCELLANEOUS PROVISIONS ..........................................    18
</TABLE>

EXHIBIT B  DEDICATION DESCRIPTION

EXHIBIT C  SAMPLE ALLOCATION AND SETTLEMENT CALCULATIONS

                                       59
<PAGE>   3
                              GAS PURCHASE CONTRACT


This Contract is entered as of July 1, 2000 between RANGE PRODUCTION I, L.P.
("Seller") and Conoco Inc. ("Buyer") and becomes effective July 1, 2000.

For and in consideration of the mutual covenants contained herein, the parties
agree as follows:

COMMITMENT.
Seller agrees to sell and Buyer agrees to purchase all of the legally produced
gas from wells now or hereafter located on all oil and gas leasehold interests
now or hereafter owned or operated by Seller on or allocated to the following
lands in Glasscock and Sterling Counties, Texas, to wit:

AS OUTLINED IN EXHIBIT B ATTACHED HERETO AND MADE A PART HEREOF BY REFERENCE
HEREIN.

The General Terms and Conditions, which are a part of this Contract, are
attached as Exhibit A and incorporated by reference.

POINTS OF DELIVERY.
The Points of Delivery of gas to be delivered by Seller to Buyer for existing
sources of production shall be at the inlet flange of Buyer's meters at mutually
agreed locations at or near the inlet of Buyer's a) North Conger compression
facilities in the NE/4 Section 10, Block 22, H&TC RR Survey, Sterling County,
TX; b) Middle Conger compression facilities in the N/2 Section 30, Block 13,
SPRR Survey, Sterling County, TX; c) South Conger compression facilities in the
N/2 Section 7, Block 21, H&TC RR Survey, Sterling County, TX; d) Ray Glass
measurement facilities in the N/2 Section 2, T&P RR Survey Block 31, T-5-S,
Sterling County, TX; and (e) Grigsby Glass measurement facilities S/2 NW/4
Section 2, Block 32 T&P RR Survey Township 5S, Glasscock County, Texas. The
Point(s) of Delivery for future sources of production will be established under
Exhibit A, Paragraph B.2. Title to the gas and all its components shall pass to
and vest in Buyer at the inlet flange of Buyer's meter at the Points of
Delivery.

DELIVERY PRESSURE AND QUANTITY.

(a)      The gas shall be delivered by Seller at the Points of Delivery at a
         pressure sufficient to enable it to enter Buyer's Facilities against
         the working pressure at reasonably uniform rates of delivery. Buyer
         will maintain a Working Pressure (Exhibit A, Para. A.2) at Points (d)
         and (e) described in Paragraph 2 no greater than 1,200 psig. Buyer will
         maintain a Working Pressure for Points (a), (b) and (c) described in
         Paragraph 2 at no greater than thirty-five (35) psig during any Day.
         Days during which the Working Pressure for a Point of Delivery exceeds
         the limits set out herein are referred to as "Excess Pressure Days". In
         order to provide for normal maintenance and repairs, Buyer shall be
         allowed up to three consecutive Excess Pressure Days per event.
         Additionally, Buyer will be allowed up to 21 consecutive Excess
         Pressure Days for each compressor or engine overhaul or replacement.

(b)      Except as otherwise herein provided, it is understood and agreed that
         Buyer will take and purchase one hundred percent (100%) of the gas
         produced and made available for sale at the Point(s) of Delivery by
         Seller. Except for reasons of force majeure (Exhibit A, Para. H), in
         the event that a greater number of Excess Pressure Days occur during a
         Month at Points (a), (b) or (c) than allowed in Paragraph 3(a) and in
         Exhibit A, Paragraph B.2, Buyer agrees to compensate Seller for excess
         delivery pressures as provided in Paragraph 3(c) herein.

(c)      During any Month when the number of Excess Pressure Days exceed the
         allowed number of Excess Pressures Days, Buyer shall waive the
         $0.265/Mcf fee deducted from settlements due Seller under Paragraph 4.4
         for the volume (in Mcf) delivered to the affected Point(s) of Delivery
         for days during which the Working Pressure exceeded 35 psig, excluding
         exempt days. In order to implement the fee waiver pursuant to this
         paragraph, Seller must notify Buyer in writing within 45 days after the
         Month in which the

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<PAGE>   4
         allowed number of Excess Pressure Days was exceeded. Buyer will
         investigate Seller's claim and make appropriate adjustment to Seller's
         payment, without interest, within 30 days of Buyer's receipt of
         Seller's notice. If Buyer has not received notice of excessive Excess
         Pressure Days within 45 days after the Month in which they are alleged
         to have occurred, no waiver or adjustment will the required.

(d)      Seller may dispose of gas not taken during events of force majeure,
         subject to Buyer's right to resume purchases at any subsequent time,
         provided however, that Seller may, upon thirty (30) days written notice
         to Buyer, release from this Contract any gas that has not been taken
         for thirty (30) days by Buyer. In the event Buyer does not take gas for
         fifteen (15) consecutive days and Seller secures a different temporary
         market, Buyer may resume purchases only upon sixty (60) days' advance
         written notice as of the beginning of a Month unless otherwise agreed.

PRICE.
CONSIDERATION.
As full consideration for the gas and all its components delivered to Buyer each
Month, Buyer shall pay Seller (a) ninety percent (90%) of the Residue Gas
Proceeds as determined under Paragraph 4.2 below from the sale of Residue Gas
Allocated to Seller, and (b) ninety percent (90%) of the NGL Proceeds determined
under Paragraph 4.3 below from the sale of any NGL's Allocable to Seller.

RESIDUE GAS PROCEEDS.
(a)      The Residue Gas Proceeds shall be determined by multiplying the MMBtu's
         of Residue Gas Allocable to Seller times the Index price published in
         Inside F.E.R.C.'s Gas Market Report for gas delivered to pipe at the
         Houston Ship Channel/Beaumont, Texas (Large Packages) less $.10/MMBtu.

(b)      Each 12-Month period beginning on November 1 during the term of this
         Contract is herein referred to as a "Pricing Period". Effective with
         the Pricing Period beginning November 1, 2000 and annually thereafter,
         either party shall have the right to require a redetermination of the
         price to be used in calculating the Residue Gas Proceeds payable to
         Seller pursuant to Paragraph 4.1. Such redetermination shall be
         requested by written notice to the other party no later than September
         1 prior to the Pricing Period for which the redetermined price is to be
         effective. The parties will then negotiate in good faith to agree upon
         a replacement price for the calculation of Residue Gas Proceeds
         hereunder. If the parties have not agreed to a redetermined price for
         such calculation by October 1, then Seller will take delivery in kind
         of 90 percent of the Residue Gas Allocated to Seller, as provided in
         Paragraph 4.6 below, during the following Pricing Period. During any
         Pricing Period when Seller is taking its share of Residue Gas in kind,
         Buyer will notify Seller by September 1 of the price that Buyer is
         willing to offer in calculating Residue Gas Proceeds during the
         subsequent Pricing Period, and Seller will have the option for such
         subsequent Pricing Period either to accept the redetermined price
         offered by Buyer or to continue taking its share of Residue Gas in
         kind.

NGL PROCEEDS.
NGL Proceeds from the sale of NGL's Allocable to Seller shall be determined by
multiplying the quantity of each NGL component allocable to Seller's gas by the
Average Price per gallon for each NGL component. The term "Average Price" as to
each NGL component shall mean the simple average of the daily average spot
prices (non-TET) for (i) purity ethane, (ii) propane, (iii) iso-butane, (iv)
normal butane, and (v) the pentanes and heavier during the Month as reported for
Mt. Belvieu, Texas by the Oil Price Information Service (or in its absence, a
comparable mutually agreed successor publication) less all actual expenses, fees
and adjustments incurred by Buyer in connection with the delivery,
transportation, fractionation and sale of such NGL's ("T&F costs"), which
equaled $0.0368 per gallon as of November 1999. Notwithstanding the foregoing,
the parties agree that from the effective date through November 30, 2000, the
T&F costs for NGL's Allocable to Seller will be $0.02848 per gallon.

                                       61
<PAGE>   5
COMPRESSION, GATHERING AND FACILITIES USE FEE.
(a)      The payment for gas delivered at Points (a), (b) and (c) described in
         Paragraph 2 as computed under Paragraphs 4.1, 4.2, and 4.3 shall be
         reduced by twenty-six and one half cents per Point of Delivery Mcf
         ($0.265/Mcf), hereinafter the "Compression, Gathering and Facilities
         Use Fee". Said Compression, Gathering and Facilities Use Fee shall
         remain unchanged from the effective date of this Contract though
         calendar year 2003. Effective January 1, 2004, and each January 1
         thereafter, the Compression, Gathering and Facilities Use Fee will be
         adjusted as provided in Paragraph 4.4(b). This will be the total of all
         charges reimbursed to Buyer to transport gas from the Point(s) of
         Delivery to Buyer's plant and to process Seller's gas delivered.

(b)      For calendar year 2004 and each calendar year thereafter, the
         Compression, Gathering and Facilities Use Fee set out in 4.4(a) will be
         multiplied by a fraction, the numerator of which will be the Consumer
         Price Index for All Urban Consumers ("CPI") for January of such
         calendar year and the denominator of which will be the CPI for January
         2000.

ALLOCATION OF RESIDUE GAS AND NGL'S.
Buyer will determine the Residue Gas and NGL's Allocable to Seller for each
component by using the calculations and definitions stated in Exhibit A,
Paragraphs A(10) A(11) and A(12). The calculations and definitions of Paragraph
4 and Exhibit A, Paragraphs A(10) A(11) and A(12), are illustrated in Exhibit C.
To the extent Exhibit C conflicts with this Agreement, then the terms and
conditions of this Agreement shall prevail.

RESIDUE GAS TAKEN IN KIND
(a)      During any Pricing Period in which Seller takes its Residue Gas in
         kind, Buyer will redeliver for Seller's account a quantity of gas (in
         MMBtu) equal to 90 percent of the Residue Gas Allocable to Seller at a
         Redelivery Point designated by Seller, provided that Seller must comply
         with the residue pipelines' nomination requirements. The Redelivery
         Point will be the interconnection of Buyer's tailgate facilities with
         the pipeline facilities of PG&E Transmission Company/Texas Utility Fuel
         Company or Lone Star Gas Company at the tailgate of Buyer's plant(s) in
         Sterling County, Texas, unless Buyer has shut down its plants in
         Sterling County and Seller's gas is being processed at another plant.
         If gas is being processed in a plant outside of Sterling County, the
         Redelivery Point will be the interconnection of the tailgate facilities
         of said plant with the residue pipelines available at said plant.
         Seller's Redelivered gas shall be of merchantable quality without
         requiring additional treatment.

(b)      During any Month that Seller takes Residue Gas in kind, then the
         parties shall cooperate to the extent operationally practical to
         eliminate any imbalance(s) between the quantity of Residue Gas that
         Seller is entitled to receive and the quantity actually delivered for
         Seller's account at the Redelivery Point by subsequent adjustments in
         gas nominations, confirmations and/or physical receipts and deliveries.
         Any imbalances remaining at the end of each Month shall be eliminated
         by cash payment for the entire amount of the imbalance as follows:

         (i)      If Seller has received more Residue Gas at the Redelivery
                  Point than due to Seller and such imbalance is not solely the
                  fault of Buyer:

                  (A)      Seller shall pay Buyer the Average Daily Index Price
                           for that portion of the imbalance which does not
                           exceed 5% of the quantity due Seller; and

                  (B)      Seller shall pay Buyer 105% of the Average Daily
                           Index Price for that portion of the imbalance, if
                           any, which exceeds 5% of the quantity due Seller, but
                           is not in excess of 10% of such quantity; and

                  (C)      Seller shall pay Buyer 110% of the Average Daily
                           Index Price for that portion of the imbalance, if
                           any, which exceeds 10% of the quantity due Seller,
                           but is not in excess of 20% of such quantity, and

                  (D)      Seller shall pay Buyer 120% of the Average Daily
                           Index Price for that portion of the imbalance, if
                           any, which exceeds 20% of the quantity due Seller.

         (ii)     If Seller has received less Residue Gas at the Redelivery
                  Point than due to Seller and such imbalance is not solely the
                  fault of Buyer:

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<PAGE>   6
                  (A)      Buyer shall pay Seller the Average Daily Index Price
                           for that portion of the imbalance which does not
                           exceed 5% of the quantity due to Seller; and

                  (B)      Buyer shall pay Seller 95% of the Average Daily Index
                           Price for that portion of the imbalance, if any,
                           which exceeds 5% of the quantity due Seller, but is
                           not in excess of 10% of such quantity; and

                  (C)      Buyer shall pay Seller 90% of the Average Daily Index
                           Price for that portion of the imbalance, if any,
                           which exceeds 10% of the quantity due to Seller, but
                           is not in excess of 20% of such quantity, and

                  (D)      Buyer shall pay Seller 80% of the Average Daily Index
                           Price for that portion of the imbalance, if any,
                           which exceeds 20% of the quantity due to Seller

         (iii)    For purposes of this Paragraph 4.6(b), the term "Average Daily
                  Index Price" shall mean the simple average of each day's price
                  for such Month as found in the Financial Times Energy
                  publication "Gas Daily," in the section entitled "Daily Price
                  Survey," for WAHA under the heading "Texas Intrastate, WAHA
                  area" under the column marked "Midpoint".

REDETERMINATION OF REFERENCE PRICE
In the event any of the published prices referenced in this Section 4 are
discontinued or materially modified, its successor shall be used, or in the
absence of a successor, Buyer and Seller shall mutually agree to another
published price reference that represents gas or NGL spot prices closely
comparable to that previously used. If a published price is discontinued or
materially modified, Buyer will inform Seller by written notice. If the parties
cannot agree on a satisfactory replacement reference price within two Months
after a reference price ceases to be published, then either party may initiate
arbitration by written notice to the other calling for the appointment of an
arbitrator to whom each party will nominate its preferred replacement reference
price. If the parties cannot agree on a single arbitrator within 20 days after
such initial notice, each party shall select its own arbitrator, and these two
arbitrators shall select a third arbitrator. The arbitrator(s) selected to act
shall have expertise in the natural gas industry, including the marketing and
pricing of natural gas and gas products, and shall be fair and impartial and
have no financial interest in the outcome of the matter to be decided. The
arbitrator(s) shall select from the two reference price nominated by the parties
the one which best reflects a fair market price for daily or monthly commitments
of natural gas or NGL's (as applicable) where the Plant(s) are located. The
price reference selected by the arbitrator(s) shall be effective retroactively
to the first Month that the lapsed reference price ceased to be published.
Seller and Buyer will share equally in any and all costs associated with said
arbitration.

TERM.
This Contract shall remain in effect for a primary term expiring January 31,
2019, and shall continue in effect from year-to-year thereafter until canceled
by either party as of the end of the primary term or thereafter by giving the
other party ninety (90) days advance written notice.

ADDRESSES AND NOTICES.
Either party may give notices to the other party or parties by first class mail
postage prepaid, by overnight delivery service, or by facsimile at the following
addresses or other addresses furnished by a party by written notice. Unless
Seller objects in writing, Buyer may also use Seller's current address for
payments.

<TABLE>
<CAPTION>
NOTICES TO SELLER
-----------------
General, Payments Operational
-----------------------------
<S>                                                 <C>
Range Production I, L.P.                             Range Production I, L.P.
Attn: Gas Marketing                                  Attn:  Engineering
P.O. Box 54320                                       500 Throckmorton St., Suite 1900
Oklahoma City, OK  73154-4320                        Fort Worth, TX  76102
(405) 947-2545 (Voice)                               (817) 870-2601 (Voice)
(405) 947-3083 (Fax)                                 (817) 870-2316 (Fax)
</TABLE>

                                       63
<PAGE>   7
<TABLE>
<CAPTION>
NOTICES TO BUYER
----------------
General, Ownership Changes                  Accounting                          Operational
--------------------------                  ----------                          ----------------------
<S>                                         <C>                                 <C>
Conoco Inc.                                 Conoco Inc.                         Conoco Inc.
Attn: Gas Supply                            Attn: Gas Plant Accounting          San Angelo BU
P. O. Box 2197                              P. O. Box 1267                      P. O. Box 2197
                                                                                Houston, TX  77252
281-293-1639 (Voice)                        580-767-4631 (Voice)                281-293-1639(Voice)
281-293-1720 (Fax)                          580-767-3705 (Fax)                  281-293-1720 (Fax)
</TABLE>

UNPROFITABILITY.
BUYER'S RIGHT TO CLAIM UNPROFITABILITY
If the purchase of gas from any Point(s) of Delivery under this Contract becomes
Unprofitable (as defined under paragraph A.17 Exhibit "A" attached hereto) ,
Buyer shall not be obligated to purchase such gas as long as such condition
exists. Buyer may invoke this provision by written notice of Unprofitability,
which shall include the economic terms under which Buyer could continue
purchasing Seller's gas. Seller must provide written notice to Buyer within 25
days of receiving said notice, whether it is electing to accept or reject
Buyer's revised terms of purchase. If such terms are accepted by Seller, Buyer
will continue purchasing Seller's gas under the revised terms effective the
Month beginning 30 days after Buyer's original notice of unprofitability. Such
revised economic terms shall remain in effect until the purchase of Seller's gas
would have been profitable for Buyer under the original economic terms for two
consecutive Months, at which time the original economic terms shall become
effective. If the revised purchase terms are not acceptable to Seller, upon
Seller's notice to Buyer, Buyer will provide transportation services to Seller
as set out in Paragraph 7.2 below. For as long as such transportation only
arrangements are in effect, Seller will have the right to terminate the Contract
effective 90 days from Buyer's receipt of written notice from Seller, unless
Buyer within 30 days receipt of Seller's termination notice, agree to restore
the original economic terms of the Contract. Such restoration of the Contract
will be effective the Month following 30 days receipt of Buyer's notice.

BUYER'S TRANSPORTATION SERVICES
Upon request by Seller pursuant to Paragraph 7.1 above, and if operationally
feasible, Buyer will transport and redeliver to the Redelivery Point(s) selected
by Seller from those identified in Paragraph 4.6 (a) an Equivalent Quantity to
that received from Buyer at the Point(s) of Delivery for a transportation fee of
$0.20 per MMBTU received at the affected Point(s) of Delivery. For any Point of
Delivery not requiring compression, "Equivalent Quantity" shall mean a quantity
of gas equal in MMBTU to that received at the Point of Delivery. For low
pressure Points of Delivery requiring compression, "Equivalent Quantity" shall
mean a quantity of gas equal in MMBTU's to that received at the Point of
Delivery less 6 percent for field fuel and line loss. Seller's Redelivered gas
shall be of merchantable quality without requiring additional treatment.

The herein stated transportation fee shall escalate according to the terms set
out in 4.4 (b). Additionally, imbalances occurring during any period that Buyer
is providing transportation services hereunder will be resolved pursuant to the
provisions of Paragraph 4.6 (b).

If Seller elects to utilize the transportation services as described herein,
Buyer will have the right to terminate this Contract, including all
transportation services at any time after six Months from the date of Buyer's
original Unprofitability notice upon 30 days written notice to Seller.

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<PAGE>   8
   IN WITNESS WHEREOF, the parties have hereto set their hands in person or by
their duly authorized officials as of the date set forth above.


SELLER:                                   BUYER:

RANGE PRODUCTION I, L.P.                  CONOCO INC.
BY: RANGE PRODUCTION COMPANY,
A DELAWARE CORPORATION,
ITS GENERAL PARTNER

By:        /s/ Chad L. Stephens           By:       /s/ Mary Ann Pearce
   ------------------------------            --------------------------------

Name:    Chad L. Stephens                 Name:     Mary Ann Pearce
     ----------------------------              ------------------------------

Title:        Sr. Vice-President          Title: Manager G & GP
      ---------------------------               -----------------------------


Executed on: June 16, 2000                Executed on: June 15, 2000


                                       65
<PAGE>   9
                                  EXHIBIT INDEX


<TABLE>
<CAPTION>
Exhibit             Description of Exhibit

<S>                 <C>
A                   General Terms and Conditions
                           a.       Definitions
                           b.       Delivery Date
                           c.       Reservations of Seller
                           d.       Metering
                           e.       Determination of Gas Composition
                           f.       Quality of Gas
                           g.       Billing and Payment
                           h.       Force Majeure
                           i.       Title, Ownership
                           j.       Royalty
                           k.       Severance and Similar Taxes
                           l.       Laws and Regulations
                           m.       Right of Way and Ingress, Egress
                           n.       Assignment
                           o.       Miscellaneous Provisions

B                   Area of Dedication of Interest

C                   Index Based Percent of Proceeds Proforma Settlement
                    Calculations
</TABLE>



Range will make the exhibits to the Gas Purchase Contract, between Range
Production I, L.P. and Conoco, Inc., available upon request.


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