<PAGE>

                                                                   EXHIBIT 10.10
                          PHASE 2 GAS SALES AGREEMENT
                          ---------------------------

        This Agreement is made as of the 14th day of September, 1987 by and
between Boundary Gas, Inc., a Delaware Corporation (herein called "Boundary"),
and those of the following fifteen (15) United States companies (which
collectively own all of the stock of Boundary) signatory hereto: The Brooklyn
Union Gas Company; Granite State Gas Transmission, Inc.; New Jersey Natural Gas
Company; Boston Gas Company; The Connecticut Light and Power Company;
Consolidated Edison Company of New York, Inc.; National Fuel Gas Supply Corp.;
Long Island Lighting Company; Connecticut Natural Gas Corporation; Essex County
Gas Company; Manchester Gas Company; Gas Service, Inc.; Valley Gas Company;
Berkshire Gas Company; and Fitchburg Gas and Electric Light Co. (herein called
individually "Repurchaser" and collectively "Repurchasers").


                             W I T N E S S E T H:

        WHEREAS, Boundary has been formed by Repurchasers to facilitate the
purchase and importation of gas from Canada, and Boundary has entered into a
certain Phase 2 Gas Purchase Contract ("Purchase Contract") dated September
14th, 1987 which provides for the sale and delivery by TransCanada PipeLines
Limited (herein called "TransCanada") and the purchase by Boundary of
330,070,000 Mcf of gas during a period ending on or before November 1, 1996 with
said quantities of gas to be received by Tennessee Gas Pipeline Company (herein
called "Tennessee") for Boundary's account at or near the existing point of
interconnection between the
<PAGE>
 
pipeline systems of TransCanada and Tennessee near Niagara Falls, Ontario; and

        WHEREAS, TransCanada has received and accepted all necessary permits,
licenses and authorizations to enable TransCanada to export, sell and deliver to
Boundary the quantities of gas specified in the Purchase Contract; and

        WHEREAS, Boundary has received and accepted all necessary certificates,
permits, licenses and authorizations to enable Boundary to import, purchase and
accept delivery of the quantities of gas as herein provided, and to resell said
quantities to the Repurchasers signatory hereto; and

        WHEREAS, Repurchasers signatory hereto have received, and each in its
sole discretion has accepted, all governmental authorizations necessary to
purchase and accept delivery of all quantities of gas sold by Boundary; and

        WHEREAS, Tennessee has received and accepted all necessary
certificates, permits, licenses and authorizations to enable Tennessee to
transport the quantities of gas purchased by Boundary from TransCanada and
resold to Repurchasers; and

        WHEREAS, Tennessee has agreed, subject to all necessary authorizations,
to construct or contract for facilities with the capacity to transport the
quantities of gas purchased by Boundary from TransCanada and resold to
Repurchasers; and

                                      -2-
<PAGE>
 
        WHEREAS, Repurchasers signatory hereto have executed or shall within
thirty (30) days hereof execute duly authorized Transportation Contracts with
Tennessee pursuant to which Tennessee agrees to transport for said Repurchasers
the quantities of gas purchased by said Repurchasers from Boundary; and

        WHEREAS, it is the intention of the parties that the gas sold by
Boundary to the Repurchasers shall be sold at Boundary's cost including
Boundary's expenses and shall not produce a profit or a loss to Boundary.

        NOW, THEREFORE, in consideration of the mutual covenants and benefits
herein contained, it is hereby agreed as follows:

                            ARTICLE I - DEFINITIONS
                            -----------------------

        All of the terms defined in the Purchase Contract and the Memorandum of
Agreement by and among Repurchasers dated October 6, 1980, as amended April 29,
1983, February 23, 1984 and April 16, 1984 and supplemented May 31, 1985 (herein
called the "Memorandum of Agreement") shall have the same meaning wherever used
in this Agreement.

               ARTICLE II - SEVERAL OBLIGATIONS OF REPURCHASERS
               ------------------------------------------------

        The duties, obligations and liabilities of Repurchasers under this
Agreement shall be the several obligations of each Repurchaser and shall not be
the joint or collective obligations of all Repurchasers.  No partnership, joint
venture, association or other relationship, other than purchasers from Boundary,
is

                                      -3-
<PAGE>
 
created by this Agreement.  No Repurchaser, as a result of participation in the
sale and purchase of gas under this Agreement, shall be prohibited in any manner
whatsoever from engaging in any business, in any transaction or in any
relationship with any entity.

                   ARTICLE III - COMMENCEMENT OF DELIVERIES
                   ----------------------------------------

        Deliveries of gas by Boundary to the Repurchasers hereunder shall
commence on the date which TransCanada commences deliveries to Boundary pursuant
to the Purchase Contract.

                        ARTICLE IV - POINT OF DELIVERY
                        ------------------------------

        The point at which the gas purchased hereunder is to be delivered by
Boundary to the Repurchasers shall be the point at which TransCanada delivers to
Tennessee for Boundary's account the gas purchased by Boundary pursuant to the
Purchase Contract.

                    ARTICLE V - TRANSPORTATION ARRANGEMENTS
                    ---------------------------------------

         Repurchasers acknowledge that Boundary owns and operates no facilities
and has no capacity or obligation to transport gas for any Repurchaser.  Each
Repurchaser shall be responsible for entering into and maintaining for the term
of this Agreement the necessary arrangements with Tennessee (or other
appropriate companies) for transportation of the volumes of gas purchased by the
Repurchaser from Boundary under this Agreement.

                                      -4-
<PAGE>
 
                               ARTICLE VI - TERM
                               -----------------

        This Agreement shall be effective from November 1, 1987 and shall remain
in full force and effect for the entire term and duration of the Purchase
Contract.

                    ARTICLE VII - SALE AND PURCHASE OF GAS
                    --------------------------------------

          1.   Boundary shall sell and deliver to Repurchasers all (100%) of the
gas purchased by Boundary from TransCanada. Boundary's sale and delivery to each
Repurchaser of said Repurchaser's respective share of the gas (as set forth
below) shall be deemed to occur simultaneously with Tennessee's receipt for
Boundary's account of the gas purchased by Boundary for resale to that
Repurchaser.

          2.   Subject to the provisions of Article VIII below, each Repurchaser
shall be entitled to purchase and accept delivery from Boundary of the following
shares ("Percentage Entitlements") of the gas purchased by and delivered to
Boundary pursuant to the Purchase Contract:

                                                      Percentage       
          Repurchaser                                 Entitlement
          -----------                                 ----------- 

          The Brooklyn Union Gas Company .............   32.40 
          Granite State Gas                             
           Transmission, Inc. ........................   13.51
          New Jersey Natural Gas Company .............   11.63
          Boston Gas Company .........................   11.31
          The Connecticut Light and Power               
           Company ...................................   10.23
          Consolidated Edison Company of                
           New York, Inc. ............................    5.40
          National Fuel Gas Supply Corp. .............    2.70 

                                      -5-
<PAGE>
 
          Long Island Lighting Company................   2.70
          Connecticut Natural Gas
            Corporation...............................   2.16
          Essex County Gas Company....................   1.74
          Manchester Gas Company......................   1.68
          Gas Service, Inc............................   1.68
          Valley Gas Company..........................   1.15
          Berkshire Gas Company.......................   1.14
          Fitchburg Gas and Electric
            Light Co..................................   0.57

          3.   It is understood and agreed that each Repurchaser will be
scheduled to receive on a daily basis as its Scheduled Daily Delivery its entire
Percentage Entitlement of the Daily Contract Quantity of gas being purchased by
Boundary from TransCanada pursuant to the Purchase Contract. Each Repurchaser
must notify Boundary or Boundary's designee at least one (1) day in advance if
it is unable or does not intend to take its entire Scheduled Daily Delivery as
aforesaid on any day.

          4.   Notwithstanding the foregoing provisions of this Article VII, it
is understood that under the Purchase Contract, for the period from November 1,
1987 through October 31, 1988, the Daily Contract Quantity shall be a quantity
(not less than 40,000 Mcf of gas per day nor more than 90,000 Mcf of gas per
day) as mutually agreed to by Boundary and TransCanada until such time as the
facilities required for delivery by TransCanada, receipt by Tennessee and
receipt by the Repurchasers of 90,000 Mcf of gas per day are constructed,
installed and made available, at which time the Daily Contract Quantity shall be
a quantity of 90,000 Mcf of gas per day and that, beginning November 1, 1988,
the Daily Contract Quantity shall be a quantity of 92,500 Mcf of gas per day
provided that the facilities required for delivery by Seller,

                                      -6-
<PAGE>
 
receipt by Tennessee and receipt by the Repurchasers of 92,500 Mcf of gas per
day are constructed, installed and made available.  It is agreed that, during
such period when the Daily Contract Quantity is a quantity of less than 92,500
Mcf of gas per day, National Fuel Gas Supply Corporation shall not be entitled
to purchase and accept delivery of gas from Boundary and each other Repurchaser
shall be entitled to purchase and accept delivery from Boundary of a share of
the gas purchased by and delivered to Boundary pursuant to the Purchase Contract
determined by dividing the Percentage Entitlement of such Repurchaser by the sum
of the Percentage Entitlements of all Repurchasers except National Fuel Gas
Supply Corporation (such share to be such Repurchaser's Percentage Entitlement
during such period for all purposes of this Agreement except Section 2. of
Article IX).

                     ARTICLE VIII - ENTITLEMENT REDUCTION
                     ------------------------------------


          1.   Repurchasers recognize that Boundary's Daily Contract Quantity
under the Purchase Contract is subject to reduction by TransCanada in
circumstances set forth therein. It is understood that any reduction by
TransCanada of Boundary's Daily Contract Quantity under the Purchase Contract
shall be borne by those Repurchasers whose actions caused or resulted in said
reduction, as determined by Section 2. of this Article VIII.

          2.   If Boundary fails to take the Annual Triggering Quantity (as
defined in the Purchase Contract) in any contract year ("Year 1") and Boundary
fails to take the Required Quantity (as defined in the Purchase Contract) in the
succeeding contract

                                      -7-
<PAGE>
 
year ("Year 2") and TransCanada elects to reduce Boundary's Daily Contract
Quantity under the Purchase Contract, the Percentage Entitlement of each
Repurchaser which during Year 1 failed to take its Annual Triggering Quantity
(as hereinafter defined) for that contract year shall be subject to reduction.
The "Annual Triggering Quantity" for each Repurchaser means the product obtained
by multiplying that Repurchaser's Percentage Entitlement times the total Daily
Contract Quantity under the Purchase Contract times the number of days in the
relevant contract year times 0.60, which product shall be adjusted to reflect
the difference, if any, between the volume requested by that Repurchaser and the
actual volume delivered on any day by Boundary to that Repurchaser, if less than
the volume requested as its Scheduled Daily Delivery, as the same occurs from
time to time during the relevant contract year. In the event that a Repurchaser
accepts volumes of gas released by another Repurchaser pursuant to Article XI
hereof, sixty percent (60%) of the volumes so accepted shall be added to the
accepting Repurchaser's Annual Triggering Quantity and deducted from releasing
Repurchaser's Annual Triggering Quantity (with an appropriate adjustment for gas
requested but not delivered). Any reduction in Boundary's Daily Contract
Quantity under the Purchase Contract shall be allocated as reductions in the
Percentage Entitlement of each Repurchaser which failed to take its Annual
Triggering Quantity in Year 1 as follows:

          (a)  The difference between each such Repurchaser's Annual Triggering
               Quantity in Year 1 and the volumes of gas

                                      -8-
<PAGE>
 
               actually purchased during Year 1 shall be deemed to be such
               Repurchaser's "Year 1 Volume Deficiency."

          (b)  The difference between each such Repurchaser's Annual Triggering
               Quantity in Year 2 plus its Year 1 Volume Deficiency and the
               volumes of gas actually purchased during Year 2 shall be deemed
               to be such Repurchaser's "Year 2 Volume Deficiency," except that,
               in the event that such calculation results in a negative number,
               the Year 2 Volume Deficiency shall be deemed to be zero and in
               the event that such calculation results in a number greater than
               the Year 1 Volume Deficiency, the Year 2 Volume Deficiency shall
               be deemed to be equal to the Year 1 Volume Deficiency.

          (c)  The sum of each such Repurchaser's Year 1 Volume Deficiency and
               Year 2 Volume Deficiency shall be deemed to be such Repurchaser's
               "Total Volume Deficiency."

          (d)  The total Volume Deficiency of each such Repurchaser shall be
               divided by the Total Volume Deficiencies of all such Repurchasers
               to determine each such Repurchaser's proportionate share of the
               reduction in Boundary's Daily Contract Quantity, and the
               Percentage Entitlement of each such Repurchaser shall be reduced
               by its proportionate share of such reduction in Boundary's Daily
               Contract Quantity.

                                      -9-
<PAGE>
 
Upon determination of the allocation of the reduction in Boundary's Daily
Contract Quantity, the respective Percentage Entitlements of all Repurchasers
shall be adjusted to reflect the relative interests in the reduced Daily
Contract Quantity, and the Memorandum of Agreement and this Agreement shall be
amended accordingly.

              ARTICLE IX - PRICE; REPURCHASER PAYMENT OBLIGATIONS
              ---------------------------------------------------

               1.   It is understood that, pursuant to Article VII of the 
Purchase Contract, the base price to be paid by Boundary to TransCanada for each
1,000,000 Btus contained in the gas delivered to Boundary by TransCanada under
the Purchase Contract shall consist of a demand charge and a seasonal commodity
charge and that the base price shall be indexed to a weighted average of
alternate fuel prices. It is further understood that, pursuant to Article VIII
of the Purchase Contract, the amount due by Boundary to TransCanada for gas
service during any contract month shall be billed to Boundary monthly by
TransCanada and shall consist of the Monthly Demand Charge and the Commodity
Charges per MMBtu of gas actually delivered during the contract month.
Consistent with the foregoing, the amount to be paid by Repurchasers to Boundary
for gas service under this Agreement shall be determined as follows:
Repurchasers in the aggregate shall pay to Boundary an amount equal to the
amount billed to Boundary by TransCanada for gas service during each contract
month. The portion to be paid by each Repurchaser to Boundary shall be equal to
the sum of (1) the product of the Monthly Demand Charge billed to Boundary by

                                      -10-
<PAGE>
 
TransCanada times such Repurchaser's Percentage Entitlement and (2) the product
of the Commodity Charges billed to Boundary by TransCanada times a fraction, the
numerator of which is the quantity of gas delivered by Boundary to such
Repurchaser during such contract month and the denominator of which is the
quantity of gas delivered by Boundary to all Repurchasers during such contract
month. For purposes of the calculation in clause (1) of the preceding sentence,
the Percentage Entitlements of each Repurchaser which takes gas pursuant to
Article XI, Section 1. (or releases gas which is so taken) shall be increased
(or decreased, as appropriate) by an amount equal to the ratio of the total
volume of gas taken (or released) by such Repurchaser during such contract month
to the product of Boundary's Daily Contract Quantity under the Purchase Contract
times the number of days in such contract month. It is further understood that
pursuant to Article VIII of the Purchase Contract any differential caused by
fluctuations in the exchange rate between the amount billed to Boundary by
TransCanada for gas service during any contract month and the amount paid by
Boundary to TransCanada for that contract month shall be reflected as a credit
or debit to the amount billed to Boundary by TransCanada for gas service during
the succeeding contract months. Consistent with the foregoing, any such credit
or a debit shall be allocated to each Repurchaser in the proportion that the
amount paid by that Repurchaser bears to the total amount paid by Boundary for
the contract month for which there was the differential resulting in the credit
or debit.

                                      -11-
<PAGE>
 
          2.   In addition to the amount payable by Repurchasers under Section
1. above, Repurchasers shall pay to Boundary all costs and expenses incurred by
Boundary in any contract month in performing this Agreement and the Purchase
Contract, including but not limited to all administrative and operating
expenses, legal fees and all taxes, including franchise taxes, sales taxes,
import duties and other taxes, duties and the like, if any, payable by Boundary
during such contract month. Each Repurchaser's shares, if any, of Boundary's
costs and expenses shall be determined by Boundary as follows:

          (i)  costs and expenses incurred by Boundary in any contract month
               which are not directly related to the quantity of gas delivered
               by Boundary to Repurchasers in that contract month shall be
               allocated among all Repurchasers on the basis of their Percentage
               Entitlements;

          (ii) costs and expenses incurred by Boundary in any contract month
               which are directly related to the quantity of gas delivered by
               Boundary to Repurchasers in that contract month shall be
               allocated to each Repurchaser in the proportion that the gas
               delivered to that Repurchaser in such contract month bears to the
               total quantity of gas delivered to all Repurchasers in such
               contract month;

                                      -12-
<PAGE>
 
          (iii)  interest expenses payable by Boundary to TransCanada in any
                 contract month pursuant to Article VIII of the Purchase
                 Contract due to late payment by Boundary shall be paid in full
                 by the Repurchaser(s) whose late payment to Boundary caused
                 such interest expenses to be incurred; and

          (iv)   costs and expenses incurred by Boundary in any contract month
                 in connection with regulatory or legal proceedings instituted
                 or joined in by Boundary on behalf of one or more (but not all)
                 Repurchasers shall be allocated to each such Repurchaser in the
                 proportion that its Percentage Entitlement bears to the total
                 Percentage Entitlements of all such Repurchasers; provided,
                 however, that in no event shall any costs and expenses incurred
                 in connection with regulatory or legal proceedings involving
                 cancellation of a Repurchaser's rights under this Agreement be
                 allocated under this subsection (iv) to the Repurchaser whose
                 rights are sought to be cancelled.

Boundary may include in its invoice to each Repurchaser for any contract month
that Repurchaser's share (determined in accordance with this Section 2.) of
costs and expenses which Boundary has determined will be incurred by Boundary in
the next succeeding contract month.  When costs and expenses are prepaid in
accordance with this Section 2., the invoice to each Repurchaser for the next

                                      -13-
<PAGE>
 
succeeding contract month shall nevertheless show that Repurchaser's share of
the costs and expenses actually incurred in that contract month but shall also
show a proper credit for the prepayment.

          3.   In addition to the amounts payable by Repurchasers under Sections
1. and 2. above, Boundary may assess each Repurchaser amounts determined
pursuant to Paragraph 2.5 of the Memorandum of Agreement.

          4.   In no event shall the amounts paid by Repurchasers to Boundary
pursuant to this Article IX result in either a profit or a loss to Boundary.

          5.   It is agreed that Boundary shall have the right to propose and to
file with appropriate United States regulatory authorities changes in the price
and provisions set forth in this Article, and the rate schedule and general
terms and conditions of Boundary's Gas Tariff imposed by United States
regulatory authorities; provided, however, that Repurchasers shall have the
right to approve or disapprove the selection of a new price regime, index or
formula under the Purchase Contract in accordance with Paragraph 2.7 of the
Memorandum of Agreement, to protest any such changes before the appropriate
United States regulatory authorities and to exercise any other rights which they
may have with respect thereto; and provided further that Boundary, prior to
proposing or filing any such changes, shall first have obtained the written
consent of TransCanada to such changes.

                                      -14-
<PAGE>
 
                             ARTICLE X - PAYMENTS
                             --------------------

          1.   Boundary shall render a monthly invoice to each Repurchaser for
all amounts due under Sections 1., 2. and 3. of Article IX of this Agreement
promptly after receipt by Boundary of its monthly statement from TransCanada for
gas service under the Purchase Contract.

          2. (a) It is understood that each month Boundary may authorize one
or more suitably qualified financial institutions with which Boundary has
entered into a Forward Cover Agreement approved in writing by TransCanada and
the Repurchasers ("Approved Institutions") to effect delivery of Canadian
dollars to TransCanada on the Due Date ("Forward Cover"). Boundary's monthly
invoice to each Repurchaser shall include such Repurchaser's share of the total
amount due in United States dollars for the Forward Cover arranged by Boundary
during the month ("Forward Cover Sum").

             (b) Each Repurchaser shall have the right in good faith to dispute
the amount of any invoice for such Repurchaser's proportionate share of the
Forward Cover Sum. Any Repurchaser raising such a dispute ("Responsible
Repurchaser") shall by noon Eastern Standard Time two business days prior to the
Due Date give Boundary notice of such dispute, stating the amount in dispute and
Boundary shall direct the Approved Institution(s) to adjust Forward Cover
accordingly. Promptly thereafter, Boundary shall give each Responsible
Repurchaser notice of such Repurchaser's share of the amount of the Forward
Cover Sum as adjusted ("Adjusted Forward Cover Sum"). After receipt of a
statement or

                                      -15-
<PAGE>
 
statements setting forth the amount of transactional proceeds or costs of
adjusting Forward Cover ("Transaction Amount"), Boundary shall set forth on the
invoice transmitted in the succeeding month to each Responsible Repurchaser such
Repurchaser's share of the Transaction Amount.  In the event that adjustment of
Forward Cover results in a Transaction Amount reflecting transactional costs,
the invoice rendered by Boundary the succeeding month to each Responsible
Repurchaser shall set forth such Repurchaser's share of the Transaction Amount
and payment shall be made by the Responsible Repurchaser to Boundary on or
before the due date indicated on that invoice.  In the event that adjustment of
Forward Cover results in a Transaction Amount reflecting transactional proceeds,
the invoice rendered by Boundary the succeeding month to each Responsible
Repurchaser shall set forth such Repurchaser's share of the Transaction Amount
and payment shall be made by Boundary to the Responsible Repurchaser within
thirty days of the invoice date.

          (c)  Payment by each Repurchaser of such Repurchaser's share of the
Forward Cover Sum (or, in the event of a dispute, such Repurchaser's share of
the Adjusted Forward Cover Sum) shall be made before 11:00 a.m. Eastern Standard
Time on the Due Date to the Escrow Agent designated by Boundary pursuant to the
Escrow Agreement between Boundary, TransCanada and Chemical Bank dated March 6,
1984, as amended and supplemented. In the event that a Repurchaser fails to make
payment to the Escrow Agent of its share of the Forward Cover Sum (or, in the
event of a dispute, its share of the Adjusted Forward Cover Sum), or any portion
thereof, when

                                      -16-
<PAGE>
 
same is due, interest thereon shall accrue at a rate of interest to be
determined in accordance with the applicable Forward Cover Agreements over the
period of time during which payment is past due, until same is paid, and any
late deposit shall include such interest as has accrued.


        3. (a) In any month in which Boundary does not effect Forward Cover
pursuant to a Forward Cover Agreement or there is no such effective Forward
Cover Agreement, Boundary's monthly invoice to each Repurchaser shall include
such Repurchaser's share of the U.S. Sum, as defined in Article VIII, Section
1(c) (ii) of the Purchase Contract. Payment by each Repurchaser of such
Repurchaser's share of the U.S. Sum shall be made before 11:00 a.m. Eastern
Standard Time on the Due Date to the Escrow Agent designated by Boundary
pursuant to the Escrow Agreement between Boundary, TransCanada and Chemical Bank
dated March 6, 1984, as amended and supplemented.

           (b) Each Repurchaser shall have the right in good faith to dispute
the amount of any invoice for such Repurchaser's proportionate share of the U.S.
Sum. Any Repurchaser raising such a dispute ("Responsible Repurchaser") shall
pay to the Escrow Agent such amounts as it concedes to be correct and Boundary
shall promptly declare a dispute to TransCanada in accordance with Section 2. of
Article VIII of the Purchase Contract. After a final determination of the amount
properly due and owing by Boundary to TransCanada, each Responsible Repurchaser
shall promptly pay to the Escrow Agent its share of the amount, if any, found to
be due.

                                      -17-
<PAGE>
 
If, as a result of a dispute raised as aforesaid, Boundary is required to
furnish any surety bond to TransCanada, such surety bond shall be furnished
timely and directly to TransCanada by the Responsible Repurchaser.

          4.   On or before the Due Date, payment by each Repurchaser of the
amounts due under Sections 2. and 3. of Article IX shall be made to Boundary.
Each Repurchaser shall have the right in good faith to dispute such amounts. The
Repurchaser declaring the dispute shall pay to Boundary the full amount of the
invoice which is, in whole or in part, the subject of the dispute. Any amount
later determined not to be due to Boundary by any Repurchaser shall be
reimbursed to such Repurchaser by Boundary or, where appropriate, by such other
Repurchaser(s) as are determined to owe the amount which has been disputed.

          5.   If the correct amounts are not paid by any Repurchaser when due,
Boundary shall, upon twelve (12) hours prior notice to such Repurchaser, have
the right to discontinue immediately deliveries of gas to such non-paying
Repurchaser and to make such gas available as excess gas to the other
Repurchasers in accordance with Article XI below; provided, however, that
Boundary shall not discontinue such deliveries without first having obtained the
written consent of TransCanada, and Boundary shall not make such gas available
as excess gas without first having given written notice to TransCanada. The
normal scheduled delivery to such non-paying Repurchaser shall not be
reinstituted until such Repurchaser pays all amounts due but, in any case, the

                                      -18-
<PAGE>
 
right of the non-paying Repurchaser to any amount of gas discontinued and made
available as excess gas shall not be restored. If the default should continue
for thirty (30) days after notice of default from Boundary to the non-paying
Repurchaser, Boundary may cancel the rights of the non-paying Repurchaser in
accordance with Article XII; provided, however, that no such cancellation shall
be effected by Boundary without first having obtained the written consent of
TransCanada. A decision by Boundary to withhold gas from a non-paying
Repurchaser shall in no event reduce that Repurchaser's Annual Triggering
Quantity for that contract year except to the extent that, if other Repurchasers
agree to take such withheld gas as available excess gas, sixty percent (60%) of
the volumes of gas so taken shall be added to the taking Repurchasers' Annual
Triggering Quantities and deducted from the non-paying Repurchaser's Annual
Triggering Quantity.

         6.  Repurchasers shall have the right to audit the books and accounts
of Boundary for purposes of determining the accuracy and sufficiency of the
amounts charged to Repurchasers hereunder. In the event an error is discovered
in any invoice rendered by Boundary, said error shall be adjusted in a
subsequent invoice or with a credit or debit memo.

                       ARTICLE XI - AVAILABLE EXCESS GAS
                       ---------------------------------

         1.  As provided in Article VII above, each Repurchaser will be
scheduled to receive on a daily basis its entire Percentage Entitlement of the
contract quantity of gas purchased by Boundary from TransCanada pursuant to the
Purchase Contract. Each

                                      -19-
<PAGE>
 
Repurchaser must notify Boundary at least one (1) day in advance if it is unable
or does not intend to take its scheduled delivery on any day.  If any
Repurchaser elects not to take, or fails to take its scheduled quantity of gas,
such quantities of gas as that Repurchaser does not take shall (subject to any
limitations in the certificate of public convenience and necessity governing
Boundary's sales hereunder) be offered by Boundary to the other Repurchasers in
proportion to their respective Percentage Entitlements.  However, the Annual
Triggering Quantity of any Repurchaser who elects not to take or fails to take
such gas shall not be reduced except to the extent that, if other Repurchasers
agree to take such available excess gas, sixty percent (60%) of the volumes so
taken shall be added to the taking Repurchasers' Annual Triggering Quantities
and deducted from the Annual Triggering Quantity of the Repurchaser which
elected not to take or failed to take the gas.

         2.  In the event that Excess Gas is made available by TransCanada to
Boundary pursuant to Sections 6. and 7. of Article II of the Purchase Contract,
Boundary shall promptly notify all Repurchasers of the availability of such
Excess Gas; provided, however, that Boundary shall give such notice at least
three (3) days in advance of the day on which such Excess Gas is intended to be
delivered. Once such notice has been given by Boundary, such Excess Gas shall be
treated for purposes of this Article XI as if it were a part of the contract
quantity. Consistent with that treatment, each Repurchaser will be scheduled to
receive its entire Percentage Entitlement of such Excess Gas and must notify

                                      -20-
<PAGE>
 
Boundary at least one (1) day in advance if it is unable or does not intend to
take its scheduled share of Excess Gas.  If any Repurchaser elects not to take,
or fails to take its scheduled quantity of Excess Gas, such quantity of Excess
Gas as that Repurchaser does not take shall be offered by Boundary to the other
Repurchasers in proportion to their respective Percentage Entitlements;
provided, however, that in no event shall any Repurchaser's Annual Triggering
Quantity under this Agreement be increased as a result of its acceptance or
rejection of such Excess Gas.

        3.  In the event that additional gas becomes available due to an
amendment to the Purchase Contract (approved, as necessary by all appropriate
regulatory authorities) which increases the contract quantity of gas, and one or
more Repurchasers elect not to take all or part of their share of the increase
in quantity, the available excess gas resulting from such election shall be made
available to the other Repurchasers in proportion to their respective Percentage
Entitlements.  Upon determination of which Repurchasers will take such available
excess gas, the respective Percentage Entitlements of all Repurchasers shall be
adjusted to reflect the relative interests in the total amended contract
quantity, and the Memorandum of Agreement and this Agreement shall be amended
accordingly.

 ARTICLE XII - CANCELLATION OF RIGHTS OF A DEFAULTING REPURCHASER
 ----------------------------------------------------------------

         In the event a Repurchaser ("Defaulting Repurchaser") fails to pay all
amounts due for gas service under this Agreement,

                                      -21-
<PAGE>
 
and such failure continues for thirty (30) days after notice of default from
Boundary, Boundary may, at its option and after receipt and acceptance of any
necessary regulatory approvals, and after first having obtained the written
consent of TransCanada, cancel the rights of the Defaulting Repurchaser under
this Agreement and the Memorandum of Agreement. Boundary shall exercise its
option to cancel and shall accept the regulatory approval(s) received in
connection with such cancellation only upon the affirmative vote of 60% of the
issued and outstanding Common Stock of Boundary; provided, however, that the
shares of Common Stock held by the Defaulting Repurchaser shall be deemed to be
voted against exercise of the option to cancel and acceptance of related
regulatory approval(s). Upon exercise by Boundary of its option to cancel (after
first having obtained the written consent of TransCanada) and after receipt and
acceptance by Boundary of all necessary regulatory approvals, the Defaulting
Repurchaser shall offer to assign all of its rights, title and interest in
Boundary to the remaining Repurchasers in proportion to their respective
Percentage Entitlements or in such other proportion as may be agreed upon by the
remaining Repurchasers. No remaining Repurchaser shall be obligated to accept
any assignment from the Defaulting Repurchaser. Any remaining Repurchaser
desiring to accept an assignment from the Defaulting Repurchaser but requiring
regulatory authorization to do so shall be given a reasonable opportunity to
obtain the necessary authorization. In the event that the remaining Repurchasers
accept assignment of less than all of the Defaulting Repurchaser's rights, title
and interest in

                                      -22-
<PAGE>
 
Boundary, cancellation of the Defaulting Repurchaser's rights under this
Agreement and the Memorandum of Agreement shall be effective only to the extent
that assignments have been accepted. As to any rights, title and interest of the
Defaulting Repurchaser not assigned to the remaining Repurchasers, the
Defaulting Repurchaser shall to that extent remain a party to this Agreement and
the Memorandum of Agreement.  Upon any assignment pursuant to this Article XII,
the respective Percentage Entitlements of all Repurchasers shall be adjusted to
reflect the assignment, and this Agreement and the Memorandum of Agreement shall
be amended accordingly.  Exercise of the rights of Boundary under this Article
XII shall not be in lieu of or extinguish any other rights, remedies or causes
of action Boundary may have in law or in equity against the Defaulting
Repurchaser arising from or relating to the default.


                           ARTICLE XIII - BANKRUPTCY
                           -------------------------

         If a Repurchaser should file a voluntary petition in bankruptcy or for
reorganization pursuant to any provision of the United States Bankruptcy Act, as
now existing or as hereafter amended, or pursuant to any other statute
applicable to such Repurchaser, or should such Repurchaser consent to the
appointment of a receiver or liquidator of such Repurchaser or of any
substantial portion of its assets, or if there should be filed a petition in
bankruptcy or reorganization, for liquidation or receivership, against such
Repurchaser pursuant to any provisions of any of said statutes and such petition
is not dismissed within

                                      -23-
<PAGE>
 
sixty (60) days after the date of such filing, then and in any of such events
Boundary shall, unless otherwise prohibited by law, have the right to terminate
such Repurchaser's participation in this Agreement by notice delivered to such
Repurchaser, whereupon all of the rights and obligations of Boundary and such
Repurchaser hereunder to each other shall cease and terminate, except with
respect to any rights and obligations accruing prior to the date of said
termination, and such Repurchaser's interest in Boundary shall be disposed of in
the same manner as specified in Article XII hereof.

                      ARTICLE XIV - TRANSFER OF INTERESTS
                      -----------------------------------

        Any Repurchaser may assign all or any part of its interest in, or rights
under this Agreement; provided, however, that no assignment of this Agreement or
of any of a Repurchaser's rights hereunder shall be made by a Repurchaser unless
such Repurchaser also transfers to the assignee an interest in such
Repurchaser's stock in Boundary equal to the Percentage Entitlement of gas under
this Agreement being transferred to such assignee and such assignee first
ratifies and becomes a party to the Memorandum of Agreement and this Agreement.
In addition, any Repurchaser may sell, transfer or assign all or any part of its
shares of stock in Boundary; provided, however, that no Repurchaser shall sell,
assign or transfer any of its shares of stock in Boundary unless the purchaser,
assignee or transferee thereof first ratifies and becomes a party to the
Memorandum of Agreement and this Agreement. Upon such sale, transfer or
assignment, this Agreement and the

                                      -24-
<PAGE>
 
Memorandum of Agreement shall, subject to the provisions of Article XIX hereof,
be amended to reflect such action. To the extent that any sale, transfer or
assignment proposed to be made pursuant to this Article XIV requires regulatory
authorization, such sale, transfer or assignment shall not be effected until all
necessary regulatory authorizations have been received and accepted. In the
event regulatory authorization for a sale, transfer or assignment pursuant to
this Article XIV is required to be obtained by Boundary, Boundary shall seek
diligently to obtain such authorization and, upon its receipt, the decision of
Boundary whether to accept such authorization shall be determined by a vote of
60% of the issued and outstanding Common Stock of Boundary. The provisions of
this Article XIV shall not be deemed to apply to any pledge of, or grant of a
security interest in, this Agreement or shares of stock in Boundary by a
Repurchaser in connection with any borrowing by, or indebtedness of, such
Repurchaser or any corporate affiliate thereof (i.e., a corporation owning,
                                                ----
owned by, or under common control with such Repurchaser); provided, however,
that any interest in said shares or this Agreement transferred pursuant to
foreclosure under such pledge or security interest shall continue to be subject
to the provisions of the Memorandum of Agreement and this Agreement and any
transferee thereunder shall be deemed to be substituted in the Memorandum of
Agreement and this Agreement for the Repurchaser which granted such pledge or
security interest.

                                      -25-
<PAGE>
 
              ARTICLE XV -  PRESSURE MEASUREMENT AND OUALITY OF GAS
              -----------------------------------------------------

        The pressure and quality of gas to be sold hereunder shall be in
accordance with the standards of pressure and quality set forth in the Purchase
Contract for gas to be sold thereunder.  The measurement of gas sold under the
Purchase Contract shall be used to determine the volumes of gas sold under this
Agreement.

        Any information obtained by Boundary pursuant to the provisions of the
Purchase Contract with respect to measurement and quality of the gas sold under
the Purchase Contract shall be promptly transmitted by Boundary to the
Repurchasers.

                 ARTICLE XVI - POSSESSION OF AND TITLE TO GAS
                 --------------------------------------------

        Upon delivery of the gas by Boundary to Repurchasers at the Point of
Delivery, title to the gas shall pass from Boundary to Repurchasers and
Repurchasers shall take possession of such gas and shall be deemed to be in
control thereof.  Boundary shall not be responsible for such gas thereafter,
regardless of anything thing which may be done, happen or arise with respect to
such gas after delivery.  Each Repurchaser understands that delivery of the gas
by Boundary to Repurchasers shall occur simultaneously with Tennessee's receipt
of such gas from TransCanada for Boundary's account, and that Boundary will
neither own nor construct any facilities in connection with this Agreement.
Notwithstanding the fact that Boundary will hold title to the gas for the
instant necessary to transfer title to Repurchasers, delivery of the gas by
TransCanada into Tennessee's facilities shall be deemed to be

                                      -26-
<PAGE>
 
delivery of the gas by Boundary to Repurchasers for purposes of determining as
between Boundary and Repurchasers when Repurchasers gain possession and control
of the gas.

                    ARTICLE XVII - WARRANTY OF TITLE TO GAS
                    ---------------------------------------

        Boundary warrants that it will, at the time of delivery, have good title
to all gas delivered by it to the Repurchasers hereunder, free and clear of all
liens, encumbrances and claims whatsoever, and that it will indemnify the
Repurchasers against and save them harmless from all suits, actions, debts,
accounts, damages, costs, losses and expenses arising from or out of adverse
claims of any or all persons with regard to said gas or to royalties, taxes,
license fees or charges thereon, which are applicable before the title to the
gas passes to the Repurchasers. Boundary further agrees that, as to the gas
delivered by Boundary to the Repurchasers hereunder, the Repurchasers shall be
entitled to all of the protections provided by the warranty of title set forth
in the Purchase Contract.

                  ARTICLE XVIII - FORCE MAJEURE AND REMEDIES
                  ------------------------------------------

        1.  Neither Boundary nor any Repurchaser shall be liable in damages to
the other for any act, omission or circumstances occasioned by or in consequence
of any event constituting force majeure and the obligations of Boundary and
Repurchasers then existing hereunder shall be excused during the period thereof
to the extent affected by such events of force majeure.  The term "force
majeure" shall mean any acts of God, strikes, lockouts,

                                      -27-
<PAGE>
 
acts of the public enemy, wars, blockades, insurrections, riots, epidemics,
landslides, lightning, earthquakes, fires, storms, floods, washouts, arrests and
restraints of rulers and peoples, civil disturbances, explosions, breakages or
accident to machinery or lines of pipe, line freeze-ups, temporary failure of
gas supply, temporary inability of Tennessee to receive gas for Boundary's
account, the binding order of any court or governmental authority which has been
resisted in good faith by all reasonable legal means, and any other cause,
whether of the kind herein enumerated, or otherwise, and whether caused or
occasioned by or happening on account of the act or omission of one of the
parties hereto which affects deliveries of gas at the Point of Delivery not
within the control of the party claiming excuse and which by the exercise of due
diligence such party is unable to prevent or overcome. A failure to settle or
prevent any strike or other controversy with employees or with anyone purporting
or seeking to represent employees shall not be considered to be a matter within
the control of the party claiming excuse. Under no circumstances will lack of
finances be construed to constitute force majeure.

     2.   Such causes or contingencies affecting the performance of this
Agreement by any party, however, shall not relieve it of liability in the event
of its concurring negligence or in the event of its failure to use due diligence
to remedy the situation and remove the cause in an adequate manner and with all
reasonable dispatch, nor shall such causes or contingencies affecting the
performance of this Agreement relieve any party from its obligation to make
payments of amounts then due hereunder

                                      -28-
<PAGE>
 
nor shall such causes or contingencies relieve any party of liability unless
such party shall give notice and full particulars of the same in writing or by
telegraph to the other parties as soon as possible after the occurrence relied
on.

     3.   If due to any cause whatsoever the capacity for deliveries from
TransCanada's transmission line is impaired so that TransCanada is unable to
deliver to Boundary the Daily Contract Quantity as provided in the Purchase
Contract, then Boundary shall not be liable to any of the Repurchasers for the
amount of gas not delivered, nor shall the Repurchasers be liable to Boundary to
pay for any volumes so curtailed.

     4.   If due to any cause whatsoever, the volume of gas to which a
Repurchaser is entitled under this Agreement is not delivered because of an
impairment in Tennessee's transmission line, Boundary shall not be liable for
any damages resulting from such volumes not being delivered.

     5.   Boundary's obligation to sell and Repurchasers' obligation to purchase
gas hereunder shall be suspended during the effectiveness of any governmental
action which results in the interruption of deliveries or which prevents,
totally or partially, the exportation of gas from Canada under the Purchase
Contract, the importation of gas into the United States under the Purchase
Contract, or the resale by Boundary to any Repurchaser under this Agreement, or
its transportation by Tennessee to any Boundary Repurchasers; provided, however,
that where the exportation, importation, resale or transportation is only
partially

                                      -29-
<PAGE>
 
prevented by the governmental action, Boundary's and Repurchaser's obligations
hereunder shall be suspended only to the extent prevented by such governmental
action.


                    ARTICLE XIX - ASSIGNMENT TO TRANSCANADA
                    ---------------------------------------

     1.   Repurchasers expressly agree that the rights conferred by this
Agreement on Boundary may be assigned, and acknowledge and consent to Article
XVI of the Purchase Contract, pursuant to which Boundary assigns its rights to
receive payments under this Agreement for certain periods to TransCanada, and by
said assignment gives TransCanada the right to proceed directly against any
Repurchaser whose default under this Agreement has caused a default by Boundary
under the Purchase Contract. Boundary and Repurchasers further recognize,
acknowledge and agree that such assignment shall not make TransCanada
responsible or accountable for any obligations, liabilities, claims and demands
arising under the Gas Sales Agreement.

     2.   Boundary and Repurchasers recognize and acknowledge that the initial
and continuing effectiveness of this Agreement without amendment, modification,
or any other change during the term of the Purchase Contract and that the
various provisions of this Agreement requiring the consent of TransCanada are
deemed to be essential to the effective protection of TransCanada's rights under
Article XVI of the Purchase Contract. Accordingly, Boundary and Repurchasers
agree that any amendment, modification or other change of this Agreement,
without the prior written consent of TransCanada or any action taken pursuant to
this Agreement which

                                      -30-
<PAGE>
 
action requires the prior written consent of TransCanada and such consent has
not been obtained, shall not be effective against TransCanada and may be treated
by TransCanada as a breach of this Agreement.


                            ARTICLE XX - REGULATION
                            -----------------------

     This Agreement and the respective obligations of the parties hereunder are
subject to all valid laws, orders, certificates, rules and regulations of duly
constituted authorities having jurisdiction over the parties hereto or the
subject matter hereof. Either Boundary or Repurchasers shall have the right to
contest the validity of any such law, order, certificate, rule or regulation and
the acquiescence therein or compliance therewith for any period of time shall
not be construed as a waiver of such right.


                     ARTICLE XXI - MEMORANDUM OF AGREEMENT
                     -------------------------------------

     This Agreement supersedes and takes the place of the Memorandum of
Agreement only with respect to the matters specifically addressed herein, but
otherwise the Memorandum of Agreement shall remain in full force and effect.


                  ARTICLE XXII - NONWAIVER AND FUTURE DEFAULT
                  -------------------------------------------

     No waiver by Boundary or any Repurchaser of any one or more defaults by the
other in the performance of any provisions of this Agreement shall operate or be
construed as a waiver of any

                                      -31-
<PAGE>
 
continuing or future default or defaults, whether of a like or of a different
character.


                           ARTICLE XXIII - AMENDMENT
                           -------------------------

     No Amendment of this Agreement shall be made except in writing signed by
all parties hereto.


                            ARTICLE XXIV - NOTICES
                            ----------------------

     Any notice permitted or required under this Agreement shall be given in
writing and delivered by telex or certified mail, return receipt requested to
the relevant party or parties at the following addresses (unless written notice
of changes in such addresses is received by all parties):

Boundary Gas, Inc.                           Long Island Lighting
110 Tremont Street                             Company
Boston, MA 02108                             175 E. Old Country Road
Attention:  James A. Rooney                  Hicksville, NY 11801

The Brooklyn Union Gas Company               Connecticut Natural Gas
195 Montague Street                            Corporation
Brooklyn, NY 11201                           P.O. Box 1500
                                             Hartford, CT 06144
Granite State Gas
  Transmission, Inc.                         Essex County Gas Company
120 Royall Street                            Hunt Road
Canton, MA 02021                             Amesbury, MA 01913
 
New Jersey Natural Gas Company               Manchester Gas Company
P.O. Box 1468                                P.O. Box 329
Wall, NJ 07719                               Manchester, NH 03105
 
Boston Gas Company                           Gas Service, Inc.
One Beacon Street                            P.O. Box 329
Boston, MA 02108                             Manchester, NH 03105
 
The Connecticut Light and                    Valley Gas Company 
  Power Company                              1595 Mendon Road
P.O. Box 270                                 Cumberland, RI 02864
Hartford, CT 06141-0270

                                      -32-
<PAGE>
 
Consolidated Edison Company                  Berkshire Gas Company
 of New York, Inc.                           115 Cheshire Road
Four Irving Place                            Pittsfield, MA 01201
New York, NY  11801
                                             Fitchburg Gas and Electric
National Fuel Gas Supply                       Light Co.
  Corp.                                      285 John Fitch Highway
10 Lafayette Square                          Fitchburg, MA 01420-8570
Buffalo, NY  14203

                          ARTICLE XXV - GOVERNING LAW
                          ---------------------------

     This Agreement shall be governed by and construed in accordance with the
laws of the State of New York.


                     ARTICLE XXVI - COUNTERPART EXECUTION
                     ------------------------------------

     This Agreement may be executed in separate, individual counterparts and all
of such executed counterparts shall together constitute one and the same
instrument.


                  ARTICLE XXVII - PRIOR AGREEMENT SUPERSEDED
                  ------------------------------------------

     This Agreement supersedes in its entirety the Gas Sales Agreement executed
on March 6, 1984 by Boundary Gas, Inc., The Brooklyn Union Gas Company, New
Jersey Natural Gas Company, Granite State Gas Transmission, Inc. and The
Connecticut Light and Power Company.

                                      -33-
<PAGE>
 
     IN WITNESS WHEREOF, this Gas Sales Agreement is executed as of the date
first above written.


ATTEST:                                 BOUNDARY GAS, INC.


/s/ [SIGNATURE ILLEGIBLE]^^             By  /s/ [SIGNATURE ILLEGIBLE]^^
----------------------------              -------------------------------------
(Seal)


ATTEST:                                 THE BROOKLYN UNION GAS COMPANY


____________________________            By_____________________________________
 (Seal)


ATTEST:                                 GRANITE STATE GAS
                                          TRANSMISSION, INC.

____________________________            By_____________________________________
 (Seal)


ATTEST:                                 NEW JERSEY NATURAL GAS COMPANY


____________________________            By_____________________________________
 (Seal)


ATTEST:                                 BOSTON GAS COMPANY


____________________________            By_____________________________________
 (Seal)


ATTEST:                                 THE CONNECTICUT LIGHT AND
                                          POWER COMPANY


____________________________            By_____________________________________
 (Seal)

                                      -34-
<PAGE>
 
     IN WITNESS WHEREOF, this Gas Sales Agreement is executed as of the date
first above written.


ATTEST:                                 BOUNDARY GAS, INC.


____________________________            By_____________________________________
 (Seal)


ATTEST:                                 THE BROOKLYN UNION GAS COMPANY


____________________________            By_____________________________________
 (Seal)


ATTEST:                                 GRANITE STATE GAS
                                          TRANSMISSION, INC.


____________________________            By_____________________________________
 (Seal)


ATTEST:                                 NEW JERSEY NATURAL GAS COMPANY


____________________________            By_____________________________________
 (Seal)


ATTEST:                                 BOSTON GAS COMPANY


/s/ [SIGNATURE ILLEGIBLE]^^             By  /s/ [SIGNATURE ILLEGIBLE]^^
----------------------------              -------------------------------------
 (Seal)


ATTEST:                                 THE CONNECTICUT LIGHT AND
                                          POWER COMPANY


____________________________            By_____________________________________
 (Seal)

                                      -34-
<PAGE>
 
                FIRST AMENDMENT TO PHASE 2 GAS SALES AGREEMENT
                ----------------------------------------------

     This Contract, to be called the First Amendment To Phase 2 Gas Sales
Agreement, is made this 1st day of January, 1990, by and between Boundary Gas,
Inc., A Delaware corporation (herein called "Boundary"); and those of the
following fifteen (15) United State companies (which collectively own all of the
stock of Boundary) signatory hereto: The Brooklyn Union Gas Company; Granite
State Gas Transmission, Inc.; New Jersey Natural Gas Company; Boston Gas
Company; Yankee Gas Services Company; Consolidated Edison Company of New York,
Inc.; National Fuel Gas Supply Corp.; Long Island Lighting Company; Connecticut
Natural Gas Corporation; Essex County Gas Company; Manchester Gas Company; Gas
Service, Inc.; Valley Gas Company; Berkshire Gas Company; and Fitchburg Gas and
Electric Light Co. (herein called individually "Repurchaser" and collectively
"Repurchasers").

                             W I T N E S S E T H:

     WHEREAS, Boundary and the Repurchasers have entered into a Phase 2 Gas
Sales Agreement for the sale of certain quantities of natural gas ("Phase 2
Volumes") from Boundary to the Repurchasers, dated September 14, 1987 ("Sales
Agreement"); and

     WHEREAS, deliveries and resale of the Phase 2 Volumes commenced on January
15, 1988, having been fully authorized by all United States and Canadian
regulatory authorities having jurisdiction; and
<PAGE>
 
     WHEREAS, Boundary and the Repurchasers have entered into a Precedent
Agreement to First Amendment to Phase 2 Gas Sales Agreement, wherein Boundary
and the Repurchasers have agreed to use their best efforts to seek and obtain
all necessary regulatory and governmental authorizations to effectuate the terms
of this First Amendment to Phase 2 Gas Sales Agreement ("Sales Amendment"); and

     WHEREAS, Boundary has received and accepted all necessary regulatory and
governmental authorizations to enable Boundary to effectuate this Gas Sales
Amendment; and

     WHEREAS, the Repurchasers have received and accepted all necessary
regulatory and governmental authorizations to enable the Repurchasers to
effectuate this Gas Sales Amendment; and

     WHEREAS, all other conditions of the Precedent Agreement to the Sales
Amendment have now been fulfilled; and

     WHEREAS, Boundary and the Repurchasers now desire and agree to amend the
Sales Agreement in the manner set forth herein, so that the terms and conditions
of the Sales Agreement are uniform and consistent in all material respects with
all contracts and regulatory authorizations governing the resale by Boundary and
transportation by Tennessee Gas Pipeline Company of the Phase 2 Volumes.

     NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained in the Sales Agreement and in this Sales

                                      -2-
<PAGE>
 
Amendment, Boundary and the Repurchasers agree to amend said Sales Agreement as
follows:


     1.   Section 1 of Article IX of the Sales Agreement is amended by deleting
the last two sentences of said Section.


     2.   Article X of the Sales Agreement is amended by deleting Section 2 of
said Article and, as a result of such deletion, by renumbering Sections 3, 4, 5
and 6 of said Section 2 to be Sections 2, 3, 4 and 5, respectively.

     3.   Section 2(a) of Article X of the Sales Agreement (subsequent to its
renumbering in accordance with paragraph 2 above) is amended by deleting the
first clause of the first sentence of said Section and by deleting the words
"U.S. Sum" and "Section 1(c) (ii)" to be found at the end of said sentence, and
substituting therefore "United States Dollar Sum" and "Section 1(a),"
respectively, and by adding the words, "and as specified in Section 1 of Article
IX of this Agreement" at the end of the said first sentence so that the first
sentence of said Section shall state: "Boundary's monthly invoice to each
Repurchaser shall include such Repurchaser's share of the United States Dollar
Sum, as defined in Article VIII, Section 1(a) of the Purchase Amendment and as
specified in Section 1 of Article IX of this Agreement."

     4.   Section 2(b) of Article X of the Sales Agreement (subsequent to its
renumbering in accordance with paragraph 2 above) is amended by deleting the
words "U.S. Sum" to be found at

                                      -3-
<PAGE>
 
the end of the first sentence of said Section and substituting therefore the
words "United States Dollar Sum" so that the relevant phrase of said sentence
shall state: " . . . the amount of any invoice for such Repurchaser's
proportionate share of the United States Dollar Sum."

     5.   Section 3 of Article X of the Sales Agreement (subsequent to its
renumbering in accordance with paragraph 2 above) is amended by adding the words
"of this Agreement" after the words and numbers "Sections 2 and 3 of Article IX"
to be found in the first sentence of said Section, so that the relevant phrase
of said sentence shall state " . . . amounts due under Sections 2 and 3 of
Article IX of this Agreement shall be made to Boundary."

     6.   This Sales Amendment shall be binding upon and inure to the benefit of
the parties hereto and their respective successors and assigns.

     7.   All terms and conditions of the Sales Agreement not referenced herein
shall remain in full force and effect.

                                      -4-
<PAGE>
 
     IN WITNESS WHEREOF, this Amendment to the Phase 2 Gas Sales Agreement is
executed as of the date first above written.


ATTEST:                                 BOUNDARY GAS, INC.


_____________________________           _______________________________________
 (Seal)


ATTEST:                                 THE BROOKLYN UNION GAS COMPANY


_____________________________           _______________________________________
 (Seal)


ATTEST:                                 GRANITE STATE GAS
                                          TRANSMISSION, INC.


_____________________________           _______________________________________
 (Seal)


ATTEST:                                 NEW JERSEY NATURAL GAS COMPANY


_____________________________           _______________________________________
 (Seal)


ATTEST:                                 BOSTON GAS COMPANY


                                        /s/ W. P. Luthern
_____________________________           ---------------------------------------
 (Seal)


ATTEST:                                 YANKEE GAS SERVICES COMPANY


_____________________________           _______________________________________
 (Seal)

                                      -5-
<PAGE>
 
                              SECOND AMENDMENT TO
                          PHASE 2 GAS SALES AGREEMENT
                          ---------------------------

     This Contract, to be called the Second Amendment To Phase 2 Gas Sales
Agreement, is made this 1st day of July, 1989, by and between Boundary Gas,
Inc., a Delaware Corporation (herein called "Boundary"); and those of the
following fifteen (15) United States companies (which collectively own all of
the stock of Boundary) signatory hereto: The Brooklyn Union Gas Company; Granite
State Gas Transmission, Inc.; New Jersey Natural Gas Company; Boston Gas
Company; Yankee Gas Services Company ("Yankee Gas"); Consolidated Edison Company
of New York, Inc.; National Fuel Gas Supply Corp.; Long Island Lighting Company;
Connecticut Natural Gas Corporation; Essex County Gas Company; Manchester Gas
Company; Gas Service, Inc.; Valley Gas Company; Berkshire Gas Company; and
Fitchburg Gas and Electric Light Co. (herein called individually "Repurchaser"
and collectively "Repurchasers").

                             W I T N E S S E T H :

     WHEREAS, Boundary, The Connecticut Light and Power Company ("CL&P") and all
the Repurchasers except Yankee Gas have entered into a Phase 2 Gas Sales
Agreement for the sale of certain quantities of natural gas from Boundary, dated
September 14, 1987 ("Sales Agreement"), to be amended pursuant to the terms of
the Precedent Agreement To First Amendment To Phase 2 Gas Sales Agreement, dated
September 14, 1988; and
<PAGE>
 
     WHEREAS, on or about July 1, 1989, CL&P will transfer or assign its retail
gas distribution franchises, the assets of its Gas Group, its entire interest in
the stock of Boundary, and all its interests, rights, and obligations under the
Sales Agreement to Yankee Gas, a newly formed company; and

     WHEREAS, in accordance with Article XIV of the Sales Agreement, Yankee Gas
will ratify and agree to become a party to the Sales Agreement and the
Memorandum of Agreement; and

     WHEREAS, Article XIV of the Sales Agreement requires that the Sales
Agreement be amended to reflect the sale, transfer or assignment to Yankee Gas;
and

     WHEREAS, Article XIX of the Sales Agreement further provides for the prior
written consent of TransCanada PipeLines, Limited ("TransCanada") to such an
amendment.

     NOW, THEREFORE, in accordance with Article XIV, XIX and XXIII of the Sales
Agreement, the parties hereto agree to amend the Sales Agreement, effective upon
CL&P's assignment or transfer of all of its stock and rights in the Sales
Agreement to Yankee Gas, as follows:

  1.   The Preamble and Article VII of the Sales Agreement are amended by
       deleting the name "The Connecticut Light and Power Company" and
       substituting therefor the name "Yankee Gas Services Company."

  2.   Article XXIV of the Sales Agreement is amended by deleting "The
       Connecticut Light and Power Company, P.O. Box 270, Hartford, CT 06141-
       0270" and substituting therefore the "Yankee Gas Services Company, P.O.
       Box 4002, Rocky Hill, CT 06067."

                                      -2-
<PAGE>
 
  3.   The Memorandum of Agreement is amended in all respects necessary to
       reflect this transfer and, as so amended, is appended hereto.

  4.   The Sales Agreement, as amended, is hereby ratified and confirmed.

  5.   This Second Amendment shall be binding upon and inure to the benefit of
       the parties hereto and their respective successors and assigns.

  6.   All terms and conditions of the Sales Agreement not referenced herein
       shall remain in full force and effect.

  7.   This Second Amendment shall be effective as of the date that CL&P assigns
       or transfers all of its stock and rights under the Sales Agreement to
       Yankee Gas.

  8.   This Second Amendment may be executed by separate, individual
       counterparts, and all of such counterparts together shall constitute one
       and the same instrument.

     IN WITNESS WHEREOF, this Second Amendment to the Phase 2 Gas Sales
Agreement is executed as of the date written above.


ATTEST:                                 BOUNDARY GAS, INC.


_____________________________           By_____________________________________
 (Seal)


ATTEST:                                 THE BROOKLYN UNION GAS COMPANY


_____________________________           By_____________________________________
 (Seal)

                                      -3-
<PAGE>
 
ATTEST:                                 GRANITE STATE GAS
                                          TRANSMISSION, INC.


_____________________________           By_____________________________________
 (Seal)


ATTEST:                                 NEW JERSEY NATURAL GAS COMPANY


_____________________________           By_____________________________________
 (Seal)


ATTEST:                                 BOSTON GAS COMPANY


/s/ [SIGNATURE ILLEGIBLE]^^             By /s/ William P. Luthern
-----------------------------             -------------------------------------
Asst. Sec'y
(Seal)


ATTEST:                                 YANKEE GAS SERVICES COMPANY


_____________________________           By_____________________________________
 (Seal)


ATTEST:                                 CONSOLIDATED EDISON COMPANY OF
                                          NEW YORK, INC.


_____________________________           By_____________________________________
 (Seal)


ATTEST:                                 NATIONAL FUEL GAS SUPPLY CORP.


_____________________________           By_____________________________________
 (Seal)

                                      -4-
<PAGE>
 
                THIRD AMENDMENT TO PHASE 2 GAS SALES AGREEMENT
                ----------------------------------------------

     This Contract, to be called the Third Amendment To Phase 2 Gas Sales
Agreement ("Third Sales Amendment"), is made this _____ day of __________, 1991,
by and between Boundary Gas, Inc., a Delaware corporation (hereinafter called
"Boundary") and those of the following fifteen (15) United States companies
(which collectively own all of the stock of Boundary) which are signatory
hereto: The Brooklyn Union Gas Company; Granite State Gas Transmission, Inc.;
New Jersey Natural Gas Company; Boston Gas Company; Yankee Gas Services Company;
Consolidated Edison Company of New York, Inc.; National Fuel Gas Supply
Corporation; Long Island Lighting Company; Connecticut Natural Gas Corporation;
Essex County Gas Company; Manchester Gas Company; Gas Service, Inc.; Valley Gas
Company; Berkshire Gas Company; and Fitchburg Gas and Electric Light Company
(herein called individually "Repurchaser" and collectively "Repurchasers").

                             W I T N E S S E T H:

     WHEREAS, Boundary and the Repurchasers have entered into a Phase 2 Gas
Sales Agreement dated September 14, 1987, as amended effective July 1, 1989 and
January 1, 1990, ("Sales Agreement") for the sale of certain quantities of
natural gas ("Phase 2 Volumes") from Boundary to the Repurchasers; and

     WHEREAS, deliveries and resale of the Phase 2 Volumes commenced on January
15, 1988, having been fully authorized by all
<PAGE>
 
United States and Canadian regulatory authorities having jurisdiction; and

     WHEREAS, Boundary and the Repurchasers entered into a Precedent Agreement
to Third Amendment To Phase 2 Gas Sales Agreement, in which Boundary and the
Repurchasers agreed to use their best efforts to seek and obtain all necessary
regulatory and governmental authorizations to effectuate the terms of the Third
Sales Amendment; and

     WHEREAS, Boundary has received and accepted all necessary regulatory and
governmental authorizations to enable Boundary to effectuate the Third Sales
Amendment; and

     WHEREAS, the Repurchasers have received and accepted any necessary
regulatory and governmental authorizations to enable the Repurchasers to
effectuate the Third Sales Amendment; and

     WHEREAS, all other conditions of the Precedent Agreement To Third Amendment
To Gas Sales Agreement have now been fulfilled; and

     WHEREAS, Boundary and the Repurchasers now desire and agree to amend the
Sales Agreement in the manner set forth herein, in order to clarify the excess
gas pricing calculation in the Sales Agreement.

     NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained in the Sales Agreement, as amended, and

                                      -2-
<PAGE>
 
in this Third Sales Amendment, Boundary and the Repurchasers agree to amend the
Sales Agreement as follows:

     1.   Article IX, Section 1., of the Sales Agreement is amended by deleting
the period (.) at the end of the fifth sentence and replacing it with a
semicolon (;), and by adding the following language: "provided, however, that if
gas released and taken pursuant to Article XI, Section 1. is taken at a price
which does not include a full aliquot share of the Monthly Demand Charge,
Boundary shall take the variation into account in performing the subject
calculation."

     2.   This Third Sales Amendment shall be binding upon and inure to the
benefit of the parties hereto and their respective successors and assigns.

     3.   All terms and conditions of the Sales Agreement not referenced herein
shall remain in full force and effect.

     IN WITNESS WHEREOF, this Third Amendment To Phase 2 Gas Sales Agreement is
executed as of the date first written above.


ATTEST:                                      BOUNDARY GAS, INC.


_______________________________              By:________________________________
 (Seal)

                                      -3-
<PAGE>
 
ATTEST:                                      THE BROOKLYN UNION GAS COMPANY


_______________________________              By:________________________________
 (Seal)


ATTEST:                                      GRANITE STATE GAS
                                               TRANSMISSION, INC.


_______________________________              By:________________________________
 (Seal)


ATTEST:                                      NEW JERSEY NATURAL GAS COMPANY


_______________________________              By:________________________________
 (Seal)


ATTEST:                                      BOSTON GAS COMPANY


                                             By:   /s/ William R. Luthern
_______________________________                 --------------------------------
 (Seal)


ATTEST:                                      YANKEE GAS SERVICES COMPANY


_______________________________              By:________________________________
 (Seal)


ATTEST:                                      CONSOLIDATED EDISON COMPANY OF
                                               NEW YORK, INC.


_______________________________              By:________________________________
 (Seal)

                                      -4-
<PAGE>
 
                              FOURTH AMENDMENT TO
                          PHASE 2 GAS SALES AGREEMENT
                          ---------------------------

     This Contract, to be called the Fourth Amendment To Phase 2 Gas Sales
Agreement, is made this 5th day of June, 1991, by and between Boundary Gas,
Inc., a Delaware Corporation (herein called "Boundary"); and those of the
following fourteen (14) United States companies (which collectively own all of
the stock of Boundary) signatory hereto: The Brooklyn Union Gas Company; Granite
State Gas Transmission, Inc.; New Jersey Natural Gas Company; Boston Gas
Company; Yankee Gas Services Company; Consolidated Edison Company of New York,
Inc.; National Fuel Gas Supply Corp.; Long Island Lighting Company; Connecticut
Natural Gas Corporation; Essex County Gas Company; EnergyNorth Natural Gas, Inc.
("EnergyNorth"); Valley Gas Company; Berkshire Gas Company; and Fitchburg Gas
and Electric Light Co. (herein called individually "Repurchaser" and
collectively "Repurchasers").

                             W I T N E S S E T H :

     WHEREAS, Boundary, Manchester Gas Company ("Manchester"), Gas Service, Inc.
("Gas Service") and all the Repurchasers except EnergyNorth have entered into a
Phase 2 Gas Sales Agreement for the purchase of certain quantities of natural
gas from Boundary, dated September 14, 1987 ("Sales Agreement"), as amended
effective July 1, 1989 and January 1, 1990, and as to be amended pursuant to the
terms of the Precedent Agreement to Third Amendment to Phase 2 Gas Sales
Agreement; and
<PAGE>
 
     WHEREAS, Manchester and Gas Service have merged into EnergyNorth,
transferring their entire interest in the stock of Boundary to EnergyNorth,
effective October 1, 1988; and

     WHEREAS, on October 6, 1980, all of the Stockholders of Boundary entered
into a Memorandum of Agreement, which was amended on April 29, 1983, February
23, 1984, April 16, 1984 and July 1, 1989, and supplemented on May 31, 1985; and

     WHEREAS, in accordance with Article XIV of the Sales Agreement, EnergyNorth
has agreed to ratify and become a party to the Sales Agreement and the
Memorandum of Agreement; and

     WHEREAS, Article XIV of the Sales Agreement requires that the Sales
Agreement be amended to reflect the transfer to EnergyNorth; and

     WHEREAS, Article XIX of the Sales Agreement further provides for the prior
written consent of Trans Canada PipeLines, Limited ("TransCanada") to such an
amendment.

     NOW, THEREFORE, in accordance with Article XIV, XIX and XXIII of the Sales
Agreement, the parties hereto agree to amend the Sales Agreement, effective as
of the date first written above as follows:

   1.   The Preamble and Article VII of the Sales Agreement are amended by
        deleting the names "Manchester Gas Company" and "Gas Service, Inc." and
        substituting therefor the name "EnergyNorth Natural Gas, Inc."

                                      -2-
<PAGE>
 
   2.   Article XXIV of the Sales Agreement is amended by deleting "Manchester
        Gas Company, P.O. Box 329, Manchester, NH 03105" and "Gas Service Inc.,
        P.O. Box 329, Manchester, NH 03105" and substituting therefore
        "EnergyNorth Natural Gas, Inc., 1260 Elm Street, Manchester, NH 03105."

   3.   The Memorandum of Agreement is being amended concurrently herewith.

   4.   The Sales Agreement, as amended, is hereby ratified and confirmed.

   5.   This Fourth Amendment shall be binding upon and inure to the benefit of
        the parties hereto and their respective successors and assigns.

   6.   All terms and conditions of the Sales Agreement not referenced herein
        shall remain in full force and effect.

   7.   This Fourth Amendment shall be effective as of the date first written
        above.

   8.   This Fourth Amendment may be executed by separate, individual
        counterparts, and all of such counterparts together shall constitute one
        and the same instrument.

                                      -3-
<PAGE>
 
     IN WITNESS WHEREOF, this Fourth Amendment to the Phase 2 Gas Sales
Agreement is executed as of the date written above.


ATTEST:                                      BOUNDARY GAS, INC.


_______________________________              By:________________________________
 (Seal)


ATTEST:                                      THE BROOKLYN UNION GAS COMPANY


_______________________________              By:________________________________
 (Seal)


ATTEST:                                      GRANITE STATE GAS
                                               TRANSMISSION, INC.


_______________________________              By:________________________________
 (Seal)


ATTEST:                                      NEW JERSEY NATURAL GAS COMPANY


_______________________________              By:________________________________
 (Seal)


ATTEST:                                      BOSTON GAS COMPANY


                                             By:  /s/ William R. Luthern
_______________________________                 --------------------------------
 (Seal)


ATTEST:                                      YANKEE GAS SERVICES COMPANY


_______________________________              By:________________________________
 (Seal)

                                      -4-
<PAGE>
 
                              FIFTH AMENDMENT TO
                          PHASE 2 GAS SALES AGREEMENT
                          ---------------------------

     This Contract, to be called the Fifth Amendment To Phase 2 Gas Sales
Agreement, is made this 4th day of May, 1993, by and between Boundary Gas, Inc.,
a Delaware Corporation (herein called ("Boundary"); and those of the following
fourteen (14) United States companies (which collectively own all of the stock
of Boundary) signatory hereto: The Brooklyn Union Gas Company; Granite State Gas
Transmission, Inc.; New Jersey Natural Gas Company; Boston Gas Company; Yankee
Gas Services Company; Consolidated Edison Company of New York, Inc.; National
Fuel Gas Distribution Corporation (('Distribution"); Long Island Lighting
Company; Connecticut Natural Gas Corporation; Essex County Gas Company;
EnergyNorth Natural Gas, Inc.; Valley Gas Company; Berkshire Gas Company; and
Fitchburg Gas and Electric Light Company (herein called individually
"Repurchaser" and collectively "Repurchasers").


                             W I T N E S S E T H :

     WHEREAS, Boundary, National Fuel Gas Supply Corporation ("Supply") and all
the Repurchasers except Distribution have entered into a Phase 2 Gas Sales
Agreement for the purchase of certain quantities of natural gas from Boundary,
dated September 14, 1987 ("Sales Agreement"), as amended effective July 1, 1989,
January 1, 1990, June 5, 1991 and November 6, 1991; and
<PAGE>
 
     WHEREAS, on October 6, 1980, all of the Stockholders of Boundary entered
into a Memorandum of Agreement, which was amended on April 29, 1983, February
23, 1984, April 16, 1984, July 1, 1989 and June 5, 1991, and supplemented on May
31, 1985; and

     WHEREAS, Supply is assigning its interest in the Sales Agreement and its
entire interest in the stock of Boundary to Distribution, its affiliate,
effective as of the date that the Federal Energy Regulatory Commission ("FERC")
makes Supply's restructuring effective; and

     WHEREAS, in accordance with Article XIV of the Sales Agreement,
Distribution has agreed to ratify and become a party to the Sales Agreement and
the Memorandum of Agreement; and

     WHEREAS, Article XIV of the Sales Agreement requires that the Sales
Agreement be amended to reflect the transfer to Distribution; and

     WHEREAS, Article XIX of the Sales Agreement further provides for the prior
written consent of TransCanada PipeLines, Limited ("TransCanada") to such an
amendment.

     NOW, THEREFORE, in accordance with Article XIV, XIX and XXIII of the Sales
Agreement, the parties hereto agree to amend the Sales Agreement, effective as
of the date that the FERC makes Supply's restructuring effective as follows:

                                      -2-
<PAGE>
 
          1.   The Preamble and Article VII of the Sales Agreement are amended
               by deleting the names "National Fuel Gas Supply Corporation" and
               "National Fuel Gas Supply Corp.," respectively, and substituting
               therefore the name "National Fuel Gas Distribution Corporation."

          2.   The first Whereas clause of the Sales Agreement is amended by
               deleting the words "November 1, 1996" and substituting therefore
               the words January 15, 2003."

          3.   Article I of the Sales Agreement is amended by deleting the words
               "and April 16, 1984" and substituting therefore the words ",
               April 16, 1984, July 1, 1989 and June 5, 1991,"

          4.   Article XXIV of the Sales Agreement is amended by deleting
               "National Fuel Gas Supply Corp., 10 Lafayette Square, Buffalo, NY
               14203" and substituting therefore "National Fuel Gas Distribution
               Corporation, 10 Lafayette Square, Buffalo, NY 14203."

          5.   The Memorandum of Agreement is being amended concurrently
               herewith.

          6.   The Sales Agreement, as amended, is hereby ratified and 
               confirmed.

                                      -3-
<PAGE>
 
          7.   This Fifth Amendment shall be binding upon and inure to the
               benefit of the parties hereto and their respective successors and
               assigns.

          8.   All terms and conditions of the Sales Agreement not referenced
               herein shall remain in full force and effect.

          9.   This Fifth Amendment shall be effective as of the date that the
               FERC makes Supply's restructuring effective.

          10.  This Fifth Amendment may be executed by separate, individual
               counterparts, and all of such counterparts together shall
               constitute one and the same instrument.


          IN WITNESS WHEREOF, this Fifth Amendment to the Phase 2 Gas Sales
Agreement is executed as of the date written above.


ATTEST:                                 BOUNDARY GAS, INC.


/s/ [ SIGNATURE ILLEGIBLE]^^            By /s/ Michael S. Lucy
-----------------------------              -----------------------------
      (Seal)

                                      -4-
<PAGE>
 
ATTEST:                                 THE BROOKLYN UNION GAS COMPANY

_______________________________         By___________________________
 (Seal)                       


ATTEST:                                 GRANITE STATE GAS TRANSMISSION, INC.


_______________________________         By___________________________
 (Seal)                       

ATTEST:                                 NEW JERSEY NATURAL GAS COMPANY


_______________________________         By___________________________
 (Seal)                       


ATTEST:                                 BOSTON GAS COMPANY


                                        By /s/ W. R. Luthern
_______________________________           ---------------------------
 (Seal)                             


ATTEST:                                 YANKEE GAS SERVICES COMPANY


_______________________________         By___________________________
 (Seal)                       


ATTEST:                                 CONSOLIDATED EDISON COMPANY OF
                                        NEW YORK, INC.


_______________________________         By___________________________
 (Seal)                       

                                      -5-
<PAGE>
 
                               SIXTH AMENDMENT TO
                          PHASE 2 GAS SALES AGREEMENT
                          ---------------------------



          This Contract, to be called the Sixth Amendment To Phase 2 Gas Sales
Agreement, is made this 9th day of September, 1993, by and between Boundary Gas,
Inc., a Delaware Corporation (herein called "Boundary"); and those of the
following fifteen (15) United States companies (which collectively own all of
the stock of Boundary) signatory hereto: The Brooklyn Union Gas Company; Bay
State Gas Company ("Bay State"); Northern Utilities, Inc. ("Northern
Utilities"); New Jersey Natural Gas Company; Boston Gas Company; Yankee Gas
Services Company; Consolidated Edison Company of New York, Inc.; National Fuel
Gas Distribution Corporation; Long Island Lighting Company; Connecticut Natural
Gas Corporation; Essex County Gas Company; EnergyNorth Natural Gas, Inc.; Valley
Gas Company; Berkshire Gas Company; and Fitchburg Gas and Electric Light Company
(herein called individually "Repurchaser" and collectively "Repurchasers").


                              W I T N E S S E T H


     WHEREAS, Boundary, Granite State Gas Transmission, Inc. ("Granite State")
and all the Repurchasers except Bay State and Northern Utilities have entered
into a Phase 2 Gas Sales Agreement for the purchase of certain quantities of
natural gas from Boundary, dated September 14, 1987 ("Sales Agreement"), as
<PAGE>
 
amended effective July 1, 1989, January 1, 1990, June 5, 1991, November 6, 1991
and May 4, 1993; and

     WHEREAS, on October 6, 1980, all of the Stockholders of Boundary entered
into a Memorandum of Agreement, which was amended on April 29, 1983, February
23, 1984, April 16, 1984, July 1, 1989, June 5, 1991, and May 4, 1993, and
supplemented on May 31, 1985; and

     WHEREAS, Granite State is assigning its interest in the Sales Agreement and
its entire interest in the stock of Boundary to its affiliates, Bay State and
Northern Utilities, effective as of the date that the Federal Energy Regulatory
Commission ("FERC") makes Granite State's restructuring effective; and

     WHEREAS, in accordance with Article XIV of the Sales Agreement, Bay State
and Northern Utilities have agreed to ratify and become parties to the Sales
Agreement and the Memorandum of Agreement; and

     WHEREAS, Article XIV of the Sales Agreement requires that the Sales
Agreement be amended to reflect the transfer to Bay State and Northern
Utilities; and

     WHEREAS, Article XIX of the Sales Agreement further provides for the prior
written consent of TransCanada PipeLines, Limited ("TransCanada") to such an
amendment.

     NOW, THEREFORE, in accordance with Article XIV, XIX and XXIII of the Sales
Agreement, the parties hereto agree to amend
     
                                       2
<PAGE>
 
the Sales Agreement, effective as of the date that the FERC makes Granite 
State's restructuring effective as follows:

     1.   The Preamble of the Sales Agreement is amended by (a) deleting the
          words "fourteen (14)" and substituting therefore the words "fifteen
          (15)", and (b) deleting the name "Granite State Gas Transmission,
          Inc." and substituting therefore the names "Bay State Gas Company;
          Northern Utilities, Inc.".

     2.   Article I of the Sales Agreement is amended by deleting the words "and
          May 4, 1993" and substituting therefore the words", May 4, 1993 and
          September 9, 1993,".

     3.   The table in Article VII, Section 2. of the Sales Agreement is amended
          by (a) deleting the entry "Granite State Gas Transmission, Inc.....
          13.51"; (b) inserting after the entry for Bonston Gas Company the
          entry "Bay State Gas Company..... 11.00"; and (c) inserting after the
          entry for EnergyNorth Natural Gas, Inc. the entry "Northern Utilities,
          Inc.... 2.51".

     4.   Article XXIV of the Sales Agreement is amended by deleting "Granite
          State Gas Transmission, Inc., 300 Friberg Parkway, Westborough, MA
          01581" and substituting therefore "Bay State Gas Company, 300 Friberg
          Parkway, Westborough, MA 01581" and

                                       3
<PAGE>
 
             "Northern utilities, Inc., 300 Friberg Parkway, Westborough, MA
             01581".

         5.  The Memorandum of Agreement is being amended concurrently herewith.

         6.  The Sales Agreement, as amended, is hereby ratified and confirmed.

         7.  This sixth Amendment shall be binding upon and inure to the benefit
             of the parties hereto and their respective successors and assigns.

         8.  All terms and conditions of the Sales Agreement not referenced
             herein shall remain in full force and effect.

         9.  This Sixth Amendment may be executed by separate, individual
             counterparts, and all of such counterparts together shall
             constitute one and the same instrument.


             IN WITNESS WHEREOF, this Sixth Amendment to the Phase 2 Gas Sales
Agreement is executed as of the date written above.


ATTEST:                                           BOUNDARY GAS, INC.


____________________________                      BY /s/ SIGNATURE ILLEGIBLE^^
                                                    ------------------------
   (Seal)

                                       4
<PAGE>
 
ATTEST:                                           THE BROOKLYN UNION GAS COMPANY

___________________________                       By ___________________________
      (Seal)


ATTEST:                                           NEW JERSEY NATURAL GAS COMPANY


___________________________                       By ___________________________
      (Seal)


ATTEST:                                           BOSTON GAS COMPANY


___________________________                       By /s/ William P. Luthern
                                                    ----------------------------
      (Seal)


ATTEST:                                           YANKEE GAS SERVICES COMPANY


___________________________                       By ___________________________
      (Seal)


ATTEST:                                           CONSOLIDATED EDISON COMPANY OF
                                                    NEW YORK, INC.

___________________________                       By ___________________________
      (Seal)


ATTEST:                                           NATIONAL FUEL GAS DISTRIBUTION
                                                    CORPORATION

___________________________                       By ___________________________
      (Seal)

ATTEST:                                           LONG ISLAND LIGHTING COMPANY

___________________________                       By ___________________________
    
                                       5
<PAGE>
 
                                                                [LOGO]

                                                  BOUNDARY GAS, INC.
                                                  ONE BOWDOIN SQUARE
                                                  BOSTON, MASSACHUSETTS 02114
                                                  TELEPHONE: (617) 227-8080
                                                  FAX:  (617) 227-2690
                                                  TELEX:  95-1459

March 8,1996


William Luthem
Boston Gas Company
One Beacon Street
Boston, MA 02108

Re:  Amendment to Boundary Gas Sales Agreement
     -----------------------------------------

Dear Mr. Luthem:

The Gas Purchase Contract between Boundary Gas, Inc. ("Boundary") and
TransCanada PipeLines Limited ("TransCanada") dated September 14, 1987, as
amended ("Purchase Contract"), has been amended to facilitate, permanently on a
firm basis, the delivery of the daily share of the Boundary volumes of National
Fuel Gas Distribution Corporation ("National Fuel") to the point of
interconnection between TransCanada and Empire State Pipeline ("Empire") at
Chippawa, Ontario.

A copy of the March 6, 1996 Letter Amendment between Boundary and TransCanada
("Letter Amendment"), is attached hereto. This amendment to the Purchase
Contract requires corresponding amendments to the Phase 2 Gas Sales Agreement
between Boundary and Boston Gas Company ("Boston Gas") dated September 14, 1987,
as amended ("Gas Sales Agreement").

Specifically, effective upon the effectiveness of the Letter Amendment, the Gas
Sales Agreement is amended as follows:


          (a) In the First Whereas Clause, the clause "and, with respect to
              the quantities to be resold to National Fuel Gas Distribution
              Corporation ("National Fuel"), by Empire State Pipeline ("Empire")
              for Boundary's account at or near the existing point of
              interconnection between the pipeline systems of TransCanada and
              Empire near Chippawa, Ontario" shall be inserted immediately after
              the words "Niagara Falls, Ontario."

          (b) The following new Whereas Clause shall be inserted after the
              present Fifth Whereas Clause: "WHEREAS, Empire has received and
              accepted
<PAGE>
 
March 8, 1996 
Page 2

              all necessary certificates, permits, licenses and authorizations
              to enable Empire to transport the quantities of gas purchased by
              Boundary from TransCanada and resold to National Fuel; and."

          (c) The following new Whereas Clause shall be inserted after the
              present Seventh Whereas Clause: "WHEREAS, National Fuel has
              executed a duly authorized Transportation Contract with Empire
              pursuant to which Empire agrees to transport for National Fuel the
              quantities of gas purchased by National Fuel from Boundary; and."

          (d) In Article IV, the clause "or, in the case of National Fuel, the
              point at which TransCanada delivers to Empire" shall be inserted
              after the word "Tennessee."

          (e) In Article V, the clause "or, in the case of National Fuel, with
              Empire" shall be inserted after the word "Tennessee."

          (f) In Article VII, Section 1, the word "Tennessee's" shall be deleted
              and the clause "by Tennessee or, in the case of National Fuel, by
              Empire" shall be inserted after the word "receipt."

          (g) In Article IX, Section 1, the following proviso shall be inserted
              at the end of the fourth sentence thereof: ", provided, however,
              that any increase or decrease in the Monthly Demand Charge or
              Commodity Charge with respect to the Chippawa Daily Contract
              Quantity, pursuant to the provisos to Sections 3 and 4,
              respectively, of Article VII of the Purchase Contract, shall be
              paid by National Fuel to Boundary."

          (h) In Article XVI, Section 1, the word "Tennessee's" shall be deleted
              and the clause "by Tennessee or, in the case of National Fuel, by
              Empire" shall be inserted after the word "receipt."

          (i) In Article XVI, Section 1, the clause "or, in the case of National
              Fuel, into Empire's facilities" shall be inserted after the words
              "into Tennessee's facilities."

          (j) In Article XVIII, Section 1, the clause "or, in the case of
              National Fuel, of Empire" shall be inserted after the words
              "inability of Tennessee."

<PAGE>
 
March 8,1996 
Page 3


          (k) In Article XVIII, Section 4, the clause "or, in the case of
              National Fuel, in Empire's transmission line" shall be inserted
              after the words "in Tennessee's transmission line."

          (1) In Article XVIII, Section 5, the clause "or by Empire to National
              Fuel" shall be inserted after the words "to any Boundary
              Repurchasers."

Please acknowledge these amendments by signing in the space provided below and
returning an executed copy to me.

Sincerely, 

Boundary Gas, Inc.

/s/ Michael S. Lucy

Michael S. Lucy
President

ACKNOWLEDGED AND ACCEPTED THIS 
15/th/ DAY OF MARCH, 1996

BOSTON GAS COMPANY


By:  /s/ [SIGNATURE ILLEGIBLE]^^
     --------------------------- 
Title:  Vice President
        ------------------------

<PAGE>
 
                                                              [LOGO]


                                                    BOUNDARY GAS, INC.
                                                    ONE BOWDOIN SQUARE
                                                    BOSTON, MASSACHUSETTS 02114
                                                    TELEPHONE: (617) 227-8080
                                                    FAX: (617) 227-2690
                                                    TELEX:  95-1459


                                 March 6, 1996



Mr. Peter Ewing
TransCanada Gas Marketing Limited,
as Agent for
TransCanada PipeLines Limited
55 Yonge Street, 11th Floor
Toronto, Ontario  M5E 1J4


         Re:  Fifth Amendment To TransCanada/Boundary 
              Phase 2 Gas Purchase Contract
              ---------------------------------------

Dear Mr. Ewing:


     Boundary Gas, Inc. ("Boundary") and TransCanada Pipelines Limited
("TransCanada") are parties to the Phase 2 Gas Purchase Contract, dated
September 14, 1987, as amended ("Purchase Contract"), which provides, inter
                                                                      -----
alia, for the delivery of gas by TransCanada to Boundary at TransCanada's point
----                                                                           
of interconnection with Tennessee Gas Pipeline Company ("Tennessee") near
Niagara Falls, Ontario for redelivery to National Fuel Gas Distribution
Corporation ("National Fuel") and fourteen other utility companies engaged in
the distribution of gas in the Northeastern United States.  This Amendment
concerns one change to the Purchase Contract.  Namely, National Fuel has
requested, and TransCanada and Boundary have agreed, to amend the Purchase
Contract to facilitate, permanently on a firm basis, the delivery of National
Fuel's daily share of the Boundary volumes to the point of interconnection
between TransCanada and Empire State Pipeline ("Empire") at Chippawa, Ontario.

<PAGE>
 
Mr. Peter Ewing
March 6, 1996
Page 2

          This letter reflects our agreement to the following amendments to the
Purchase Contract:

          1.   The First Whereas Clause is amended as follows:

               (a)  by deleting the words "a point" and substituting the word
"points" therefore;

               (b)  by deleting the term "'Point of Interconnection'" and
substituting the term "'Tennessee Point of Interconnection'" therefore; and

               (c)  by adding the following clause after the new term "Tennessee
Point of Interconnection":

          , and near Chippawa, Ontario, where it interconnects with the
          facilities of Empire State Pipeline ("Empire"), herein called "Empire
          Point of Interconnection" (the Tennessee Point of Interconnection and
          the Empire Point of Interconnection together, herein called "Points of
          Interconnection")

          2.   The Third Whereas Clause is deleted and the following clause is
substituted therefore:

          WHEREAS, Tennessee and Empire (herein called "U.S. Transporters") own
          and operate natural gas transmission pipeline systems in the United
          States, which interconnect with Seller's pipeline system at the
          aforementioned Points of Interconnection; and

          3.   The Fourth Whereas Clause is amended as follows:

               (a)  by deleting the words "Tennessee has" and substituting the
words "U.S. Transporters have" therefore; and

               (b)  by deleting the word "Point" and substituting the word
"Points" therefore.

<PAGE>
 
Mr. Peter Ewing
March 6, 1996
Page 3


          4.   Article 1, Section 10, "Daily Contract Quantity" is amended by
adding the following sentence after the second sentence:

          For the purpose of calculating the Monthly Demand Charge provided for
          in Section 3 of Article VII hereof, and for the purpose of defining
          the Scheduled Daily Delivery at the Points of Delivery, the Daily
          Contract Quantity at the Tennessee Point of Interconnection shall be
          deemed to be equal to the Daily Contract Quantity defined above less
          2,497.5 Mcf (the "Niagara Daily Contract Quantity") and the Daily
          Contract Quantity at the Empire Point of Interconnection shall be
          deemed to be equal to 2,497.5 Mcf (the "Chippawa Daily Contract
          Quantity").

          5.   Article III, Points of Delivery, is amended as follows:

               (a)  by deleting the word "POINT" in the title and substituting
     the word "POINTS" therefore;

               (b)  by adding before the words "Point of Interconnection" in the
     first sentence the words "Empire Point of Interconnection for the Chippawa
     Daily Contract Quantity and shall be the Tennessee";

               (c)  by adding after the words "for the account of Buyer" in the
     first sentence the words "for the Niagara Daily Contract Quantity";

               (d)  by deleting the word "Tennessee" at each place that it
     appears in the second sentence and substituting the words "U.S.
     Transporters" therefore; and

               (e)  by deleting the word "Tennessee's" in the second sentence
     and substituting the word "U.S. Transporters'" therefore.


<PAGE>
 
Mr. Peter Ewing
March 6, 1996
Page 4


     6.   Article IV, Delivery Pressure, is amended by adding after the words
"700 pounds per square inch gauge" the words "at the Tennessee Point of
Interconnection, and not less than 1225 pounds per square inch gauge at the
Empire Point of Interconnection."

     7.   Article VII, Price, Section 3 (as amended) is amended as follows:

          (a) by deleting the words "point of delivery" in subsection (i) of the
first paragraph and substituting the words "Tennessee Point of Interconnection"
therefore;

          (b) by deleting the "." at the end of subsection (iii) of the first
paragraph and substituting a ";" therefore;

          (c) by inserting before the last sentence of the first paragraph the
following proviso:

     provided, however, that the Monthly Demand Charge shall be increased 
     or decreased, as appropriate, by an amount equal to the product of 
     the Chippawa Daily Contract Quantity and the difference between the 
     monthly demand tolls (including the monthly demand component of the 
     delivery pressure tolls) per Mcf as determined by Canada's National 
     Energy Board and in effect on the first day of the month applicable 
     to the transportation of firm gas on Seller's system to the Tennessee 
     and Empire Points of Interconnection.;

     and

          (d) by inserting after the words "Demand Charge Rate" at the beginning
of the second paragraph the clause ", and, with respect to the proviso in the
preceding paragraph, the difference between the monthly demand tolls per Mcf on
Seller's system to the Tennessee and Empire Points of Interconnection,".
<PAGE>
 
Mr. Peter Ewing
March 6, 1996
Page 5


     8.   Article VII, Price, Section 4, is amended by deleting the period and
inserting the following new proviso at the end thereof:

     ; provided, however, that the Commodity Charge in respect of the
     Chippawa Daily Contract Quantity shall be increased or decreased,
     respectively, by (i) the differential calculated in accordance with 
     the proviso in Section 3 above, (ii) an amount equal to the amount 
     by which the commodity toll applicable to the firm transportation 
     of gas to the Empire Point of Interconnection exceeds or is less than 
     the commodity toll applicable to the firm transportation of gas to the 
     Tennessee Point of Interconnection [Niagara], (iii) an amount equal to 
     the amount by which the commodity component of the delivery pressure 
     toll applicable to the firm transportation of gas to the Empire Point 
     of Interconnection exceeds or is less than the commodity component of 
     the delivery pressure toll applicable to the firm transportation of 
     gas to the Tennessee Point of Interconnection and (iv) an amount equal 
     to the product of the commodity charge, as otherwise determined for the
     Tennessee Point of Interconnection, and the differential between the
     fuel requirement applicable to the firm transportation of gas to the
     Empire and Tennessee Points of Interconnection, calculated per MMbtu.

     9.   Article VIII, Billings and Payment, is amended by adding the words "at
each Point of Delivery" after the words "daily and total quantity of gas
delivered hereunder" in the first sentence of Section 1(a) and in the second
sentence of Section 1(b).

     10.  Article IX, Quality, is amended by deleting the phrase "Point of
Delivery" in the first sentence of Section 1 and substituting the phrase "Points
of Delivery" therefore.
<PAGE>
 
Mr. Peter Ewing
March 6, 1996
Page 6


     11.  Article X, Measurement of Gas, is amended as follows:

          (a)  by deleting the phrase "Point of Delivery" at each place that it
appears and substituting the phrase "Points of Delivery" therefore;

          (b)  by deleting the word "Tennessee" at each place that it appears
and substituting the words "U.S. Transporters" therefore; and

          (c)  by deleting the word "its" in Section 3. (b) and substituting the
word "their" therefore.

     12.  Article XII, Force Majeure, is amended as follows:

          (a)  by deleting the word "Tennessee" at each place that it appears
and substituting the words "U.S. Transporters" therefore;

          (b)  by deleting the words "the Point of Delivery" in the second
sentence of Section 1 and substituting the words "a Point of Delivery"
therefore; and

          (c)  by deleting the words "Point of Delivery" at both places that
they appear in Section 3 and substituting the words "Points of Delivery"
therefore.

          The effectiveness of these amendments is subject to (i) obtaining such
changes as are appropriate to the long term import and export authorizations
currently held in connection with the Purchase Contract and (ii) the receipt of
any necessary approvals from the Federal Energy Regulatory Commission ("FERC")
for related changes that must be made to Boundary's FERC Gas Tariff. Boundary
and TransCanada agree that they will use their best commercially reasonable
efforts to seek to obtain and cause the other to seek to obtain the regulatory
and governmental authorizations necessary to effectuate the terms of this Fifth
Amendment.
<PAGE>
 
Mr. Peter Ewing
March 6, 1996
Page 7


          This letter agreement shall be binding upon and inure to the benefit
of the parties hereto and their respective successors and assigns.

          If this letter agreement properly states our agreement, please
acknowledge that fact by signing in the space below and returning an executed
copy to me.

                                                  Sincerely,

                                                  Boundary Gas, Inc.

                                                  /s/ Michael S. Lucy

                                                  Michael S. Lucy
                                                  President



ACKNOWLEDGED AND ACCEPTED THIS 
12 DAY OF March, 1996



TRANSCANADA PIPELINES LIMITED


By:      /s/ Joel G. Johnson
       ----------------------------------
             JOEL G. JOHNSON 

Title:   Vice President, Marketing
       ----------------------------------



By:      /s/ G. Lawrence Spackman
       ----------------------------------
             G. LAWRENCE SPACKMAN  

Title:            President
       ----------------------------------
<PAGE>
 
                                 AMENDMENT TO
                          PHASE 2 GAS SALES AGREEMENT
                          ---------------------------

     This Contract, to be called Amendment to Phase 2 Gas Sales Agreement, is
made as of this 20th day of August, 1997 by and between Boundary Gas, Inc., a
Delaware corporation (herein called "Boundary") and the following fifteen (15)
United States companies signatory hereto (which collectively own all of the
stock of Boundary): The Brooklyn Union Gas Company, Bay State Gas Company,
Northern Utilities, Inc., New Jersey Natural Gas Company, Boston Gas Company,
Yankee Gas Services Company, Consolidated Edison Company of New York, Inc.,
National Fuel Gas Distribution Corporation, Long Island Lighting Company,
Connecticut Natural Gas Corporation, Essex County Gas Company, EnergyNorth
Natural Gas, Inc., Valley Gas Company, Berkshire Gas Company, and Fitchburg Gas
and Electric Light Company (herein collectively called "Repurchasers").

                             W I T N E S S E T H :

     WHEREAS, the Gas Purchase Contract between Boundary and TransCanada
PipeLines Limited ("TransCanada") dated September 14, 1987, as amended ("Gas
Purchase Contract"), has been amended, in pertinent part, to reflect changes
agreed upon in the resolution of certain pricing disputes between Boundary and
TransCanada (a copy of which amendment is attached hereto);
<PAGE>
 
     WHEREAS, the amendments to the Gas Purchase Contract involve the
implementation of a U.S. pipeline rate refund protocol and impose a time
limitation for adjusting overcharges and undercharges under the Gas Purchase
Contract;

     WHEREAS, these amendments require corresponding amendments to the Gas Sales
Agreement among Boundary and the Repurchasers dated September 14, 1987, as
amended ("Gas Sales Agreement");

     NOW THEREFORE, the parties hereto agree to amend the Gas Sales Agreement,
effective as of the date of the amendments to the Gas Purchase Contract, as
follows:

          1.   Article X, Section 5 shall be amended by inserting the 
               phrase "and claimed within twelve (12) months of the date 
               payment is due under the invoice containing such error" 
               immediately after the word "Boundary," on the penultimate 
               line thereof.

          2.   Effective as of November 1, 1995, the Gas Sales Agreement 
               is deemed amended as necessary to permit the implementation      
               of the protocol entitled "Treatment of Increases in U.S. 
               Pipeline Rates in the Calculation of the Price of Gas Pursuant 
               to Article VII" and attached to an amending agreement between 
               Alberta Northeast Gas Limited and TransCanada dated November 
               17, 1995.

     IN WITNESS WHEREOF, this Amendment to the Phase 2 Gas Sales Agreement is
executed as of the date written above.

                                       2
<PAGE>
 
ATTEST:                                      FITCHBURG GAS AND ELECTRIC
                                              LIGHT COMPANY


_______________________________              By_________________________________
(Seal)


ATTEST:                                      BAY STATE GAS COMPANY


_______________________________              By_________________________________
(Seal)


ATTEST:                                      NORTHERN UTILITIES, INC.


_______________________________              By_________________________________
(Seal)


ATTEST:                                      BOSTON GAS COMPANY


                                             By  /s/ William R. Luthern
_______________________________                ---------------------------------
(Seal)

                                       5