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                                PROMISSORY NOTE

                                                                  May 28, 1998

     FOR VALUE RECEIVED, MARKETSPAN CORPORATION, MARKETSPAN GAS CORPORATION
(d/b/a BROOKLYN UNION), MARKETSPAN TRADING SERVICES LLC, MARKETSPAN GENERATION
LLC, MARKETSPAN CORPORATE SERVICES LLC, MARKETSPAN UTILITY SERVICES LLC, and
MARKETSPAN ELECTRIC SERVICES LLC, each a New York corporation or limited
liability company, with its principal place of business at 175 East Old
Country Road, Hicksville, New York 11801, and MARKETSPAN FINANCE
CORPORATION, a Vermont corporation (collectively, the "Obligors"), hereby
jointly and severally promise to pay to LONG ISLAND LIGHTING COMPANY, a New
York corporation, with its principal place of business at 333 Earle Ovington
Boulevard, Suite 403, Uniondale, New York 11553 (the "Obligee") the principal
amount of TWO HUNDRED SEVENTY MILLION Dollars ($270,000,000.00) (as such
amount may be reduced to reflect the aggregate principal amount of Debentures
(as defined below) outstanding following an exchange offer by MarketSpan
Corporation therefor), on February 15, 2023 and to pay interest thereon from
February 15, 1998, semi-annually on February 15 and August 15 in each year
commencing August 15, 1998, at a rate per annum equal to 8.20%, until the
principal hereof is paid.

     This Promissory Note is one of a series of Promissory Notes issued
pursuant to the purchase price adjustment provisions of Section 2.1 of the
Agreement and Plan of Merger dated as of June 26, 1997 by and among MarketSpan
Corporation (formerly known as BL Holding Corp.), the Obligee, Long Island
Power Authority and LIPA Acquisition Corp., as amended and/or supplemented
through the date hereof (as so amended and/or supplemented, the "Merger
Agreement"), and is subject to the terms and provisions thereof. Upon the
occurrence of a Material Decline in Parent's Credit Standing (as such term is
defined in Section 2.1(f)(ii) of the Merger Agreement) this Promissory Note
(i) shall be secured by a letter of credit provided by MarketSpan Corporation,
at its sole cost and expense, and (ii) may be economically defeased by
MarketSpan Corporation, in each case as provided under Section 2.1(f) of the
Merger Agreement.

     The terms and conditions of this Promissory Note shall be determined by
reference to the debt and other obligations of the Obligee under the
Debentures, 8.20% Series Due 2023, which were issued by the Obligee under the
First Supplemental Indenture, dated as of March 1, 1993, to the Indenture
between the Obligee and The Chase Manhattan Bank (as successor to Chemical
Bank), as Trustee, dated as of November 1, 1992 (the "Debentures"). All
provisions of the Debentures relating to the payment by the Obligee of
principal, interest, premium and any other amounts payable thereunder,
including, without limitation, all provisions relating to any acceleration of
any such payment obligations for any reason, are hereby incorporated herein
and made a part hereof, except that, for purposes of such incorporation by
reference, (i) all references to the "Company" shall be deemed to be
references to the Obligors, (ii) all references to the "Holders" or the
"Trustee" shall be deemed to be references to the Obligee, (iii) all
references to the "Securities" shall be deemed to be references to this
Promissory Note and (iv) all dates



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specified therein for payments shall be deemed to be the respective dates
thirty (30) days prior thereto. In addition to the events and circumstances
included in the definition of the term "Events of Default" incorporated herein
from the Debentures, such term, as used in this Promissory Note, shall include
the occurrence of any Event of Default under the Debentures.

     Each of the Obligors hereby waives presentment for payment, demands,
notice of dishonor and protest of this Promissory Note and any right to assert
setoff of any of its obligations hereunder against any amounts owing by the
Obligee thereto. The Obligors further agree that none of the terms or
provisions of this Promissory Note may be waived, altered, modified or amended
except as the Obligee may consent in a writing duly signed for and on its
behalf. The Obligee agrees that it shall not agree to any alteration,
modification or amendment of any of the Debentures in any way that would
increase the payment obligations of the Obligees hereunder, without the prior
written consent of MarketSpan Corporation. No failure or delay on the part of
the Obligee in exercising any of its right, powers or privileges hereunder
shall operate as a waiver thereof, nor shall a single or partial exercise
thereof preclude any other or further exercise of any right, power or
privilege. The remedies provided herein are cumulative and not exclusive of
any remedies provided by law.

     The Obligors agree to pay on demand any and all reasonable out-of-pocket
costs and expenses (including reasonable fees and expenses of counsel)
incurred by the Obligee and its successor and assigns in enforcing this
Promissory Note.

     This Promissory Note is binding upon the Obligors and their successors
and assigns and is for the benefit of the Obligee and its successors and
assigns. The Obligors may not, without the prior written consent of the
Obligee, assign or otherwise transfer their obligations under this Promissory
Note.

     This Promissory Note has been delivered in the State of New York and
shall be construed and enforced in accordance with the internal and
substantive laws of such State without giving effect to the choice of law
rules.

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<PAGE>


                                     MARKETSPAN CORPORATION

                                     By: /s/ Kathleen A. Marion
                                         ----------------------
                                         Name: Kathleen A. Marion
                                         Title: Secretary and Vice President

                                     MARKETSPAN GAS CORPORATION


                                     By: /s/ Kathleen A. Marion              
                                         ---------------------              
                                         Name: Kathleen A. Marion          
                                         Title: Secretary and Vice President
                                     

                                     MARKETSPAN TRADING SERVICES LLC


                                     By: /s/ Kathleen A. Marion              
                                         ---------------------              
                                         Name: Kathleen A. Marion          
                                         Title: Secretary and Vice President
                                     

                                     MARKETSPAN GENERATION LLC


                                     By: /s/ Kathleen A. Marion              
                                         ---------------------              
                                         Name: Kathleen A. Marion          
                                         Title: Secretary and Vice President
                                     

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<PAGE>


                                     MARKETSPAN CORPORATE SERVICES LLC


                                     By: /s/ Kathleen A. Marion              
                                         ----------------------              
                                         Name: Kathleen A. Marion          
                                         Title: Secretary and Vice President
                                     

                                     MARKETSPAN UTILITY SERVICES LLC


                                     By: /s/ Kathleen A. Marion              
                                         ----------------------              
                                         Name: Kathleen A. Marion          
                                         Title: Secretary and Vice President
                                     

                                     MARKETSPAN ELECTRIC SERVICES LLC


                                     By: /s/ Kathleen A. Marion              
                                         ----------------------              
                                         Name: Kathleen A. Marion          
                                         Title: Secretary and Vice President
                                     

                                     MARKETSPAN FINANCE CORPORATION


                                     By: /s/ Kathleen A. Marion              
                                         ----------------------              
                                         Name: Kathleen A. Marion          
                                         Title: Secretary and Vice President
 

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