EXHIBIT 99(B)

                                                              December 31, 2001

Carlson Capital, L.P.
2100 McKinney Avenue, Suite 1600
Dallas, Texas 75210

Dear Sirs:

     This letter sets forth the agreement of Carlson Capital, L.P., acting on
behalf of the funds listed in Schedule "A" attached hereto (the "Purchasers"),
and MDU Resources Group, Inc. (the "Company") regarding the purchase by the
Purchasers from the Company of the Company's common stock (the "Common Stock")
on the date hereof. The parties agree as follows:

1.   This Agreement relates to the purchase by the Purchasers of an aggregate of
     379,376 shares of the Company's Common Stock (the "Shares") for an
     aggregate purchase price of $10,000,000, which purchase is being settled by
     the parties on the date hereof.

2.   The Company is a corporation duly incorporated, validly existing and in
     good standing under the laws of Delaware. The Company has the requisite
     corporate power and authority to enter into and perform this Agreement and
     to issue and sell the Shares in accordance with the terms hereof. The
     execution, delivery and performance of this Agreement by the Company and
     the consummation by it of the transactions contemplated hereby have been
     duly and validly authorized by all necessary corporate action of the
     Company. This Agreement has been duly executed and delivered on behalf of
     the Company by a duly authorized officer.

3.   The Shares to be issued under this Agreement have been duly authorized for
     issuance and sale by all necessary corporate action of the Company and,
     when issued and delivered in accordance with the terms hereof against
     payment of the consideration set forth herein, the Shares shall be validly
     issued, fully paid and nonassessable. The Shares will be issued pursuant to
     and in compliance with the resolutions, adopted August 15, 2001, of the
     Finance Committee of the Board of Directors of the Company, copies of which
     were previously delivered to the Purchasers.

4.   The Company represents and warrants that (a) the Company has filed with the
     Securities and Exchange Commission (the "Commission") pursuant to Rule 415
     under the Securities Act of 1933, as amended (the "Securities Act"), a
     registration statement on Form S-3, Commission File Number 333-49472, which
     includes a prospectus forming a part thereof, as amended and supplemented
     (the "Prospectus"), (such registration statement, as amended and
     supplemented, shall be referred to hereinafter as the "Registration
     Statement"); (b) the Company has filed a prospectus supplement to the
     Registration Statement in connection with this transaction (the "Prospectus
     Supplement"); and (c) the Shares are registered under the Registration
     Statement. Copies of the Registration Statement and the Prospectus





     Supplement, as filed (and declared effective, if applicable) by the
     Commission, are annexed hereto as Exhibits A and B, respectively.

5.   The Company will use its best efforts to list the Shares of Common Stock
     for trading on the New York Stock Exchange and the Pacific Exchange.

6.   As of their respective dates, each of the documents incorporated by
     reference in the Registration Statement and the Prospectus (the "Commission
     Filings") complied in all material respects with the requirements of the
     Securities Exchange Act of 1934 (the "Exchange Act") and the rules and
     regulations of the Commission promulgated thereunder, and, as of the date
     hereof, the Commission Filings, when read together with the other
     information in the Prospectus, does not contain any untrue statement of a
     material fact or omit to state a material fact required to be stated
     therein or necessary in order to make the statements therein, in light of
     the circumstances under which they were made, not misleading.

7.   The Company will promptly notify the Purchasers of (a) any stop order or
     other suspension of the effectiveness of either or both of the Registration
     Statement and (b) the happening of any event as a result of which the
     prospectus included in the Registration Statement includes an untrue
     statement of a material fact or omits to state a material fact required to
     be stated therein, or necessary to make the statements therein, in light of
     the circumstances under which they were made, not misleading.

8.   Except as otherwise required by applicable law or regulation or
     requirements of the New York Stock Exchange or Pacific Exchange, the
     Company may not issue a press release or otherwise make a public statement
     or announcement with respect to the completion of the transaction
     contemplated hereby without the prior consent of the Purchasers, which
     shall not be unreasonably withheld.

9.   The Company and the Purchasers will indemnify the other party(ies) as
     provided in Schedule "B" attached hereto. For purposes of said Schedule B,
     capitalized terms used therein without definition shall have the same
     meanings therein as are ascribed to said terms in this Agreement.

10.  This Agreement shall be governed and construed in accordance with the
     substantive laws of the State of New York without giving effect to the
     conflicts of law principles thereunder. This Agreement constitutes the
     entire agreement between the parties with respect to the subject matter
     hereof and supersedes all prior agreements and undertakings, both written
     and oral, among the parties, or any of them, with respect to the subject
     matter hereof. This Agreement may be executed in two or more counterparts,
     and by the different parties hereto in separate counterparts, each of which
     when executed shall be deemed to be an original but all of which taken
     together shall constitute one and the same agreement.

11.  The Purchasers have the requisite power and authority to enter into and
     perform this Agreement and to purchase the Shares in accordance with the
     terms hereof. The execution, delivery and performance of this Agreement by



                                       2


     the Purchasers and the consummation by them of the transactions
     contemplated hereby have been duly and validly authorized by all necessary
     action. This Agreement has been duly executed and delivered on behalf of
     the Purchasers by a duly authorized signatory.

12.  Each of the Purchasers represents and warrants that it is not, and will not
     as a result of its purchase of the Shares be a "Related Party," as defined
     in Section 312 of the New York Stock Exchange's Listed Companies Manual.

13.  If any provision of this Agreement shall be invalid or unenforceable in any
     jurisdiction, such invalidity or unenforceability shall not affect the
     validity or enforceability of the remainder of this Agreement in that
     jurisdiction or the validity or enforceability of any provision of this
     Agreement in any other jurisdiction.

14.  No provision of this Agreement may be amended other than by an instrument
     in writing signed by the Company and the Purchasers and no provision hereof
     may be waived other than by an instrument in writing signed by the party
     against whom enforcement is sought.

     Delivery of an executed copy of a signature page to this Agreement by
facsimile transmission shall be effective as delivery of a manually executed
copy of this Agreement and shall be effective and enforceable as the original.



                                       3



         Please execute a copy of this letter which, when executed by the
Purchasers, will constitute an Agreement between the Company and the Purchasers.

                           Very truly yours,

                           MDU RESOURCES GROUP, INC.



                           By:      /s/ Vernon A. Raile
                              ----------------------------------------
                           Name:    Vernon A. Raile
                           Title:   Vice President, Controller
                                    and Chief Accounting Officer

AGREED TO:

PURCHASERS:

CARLSON CAPITAL, L.P.

         On behalf of the funds listed in
         Schedule "A" attached hereto


By:      /s/Clint Carlson
         ---------------------------
         Authorized Signatory








                                  SCHEDULE "A"

                                   PURCHASERS



Carlson Capital, L.P., acting on behalf of the following funds:

                                              NUMBER OF SHARES     PURCHASE
           NAME OF FUND                       TO BE PURCHASED        PRICE
           ------------                       ---------------        -----

Black Diamond Offshore Ltd.                        45,117        $1,189,242.33
Double Black Diamond Offshore LDC                 234,265         6,175,008.44
Black Diamond Energy Offshore LDC                  37,934           999,905.11
Black Diamond Relative Value Offshore LDC          32,943           868,346.97
Black Diamond Capital I, Ltd.                      12,256           323,056.81
Worldwide Transactions Ltd.                        16,861           444,440.34

                       Total                      379,376       $10,000,000.00
                                                  =======       ==============







                                  SCHEDULE "B"

                            TERMS OF INDEMNIFICATION


(a)  INDEMNIFICATION BY THE COMPANY. The Company will indemnify and hold
     ------------------------------
     harmless the Purchasers and each person, if any, who controls the
     Purchasers within the meaning of Section 15 of the Securities Act of 1933,
     as amended (the "Securities Act"); or Section 20(a) of the Securities
     Exchange Act of 1934, as amended (the "Exchange Act"); from and against any
     losses, claims, damages, liabilities, costs and expenses (including,
     without limitation, reasonable costs of defense and investigation and all
     attorneys' fees and expenses) to which the Purchasers and each person, if
     any, who controls the Purchasers may become subject, under the Securities
     Act or otherwise, insofar as such losses, claims, damages, liabilities and
     expenses (or actions in respect thereof) arise out of or are based upon (i)
     any untrue statement or alleged untrue statement of a material fact
     contained, or incorporated by reference, in the Registration Statement
     relating to Shares being sold to the Purchasers (including the prospectus
     dated November 17, 2000, the ("Prospectus"), the prospectus supplement
     dated December 31, 2001 (the "Prospectus Supplement"), which is a part of
     the Registration Statement), or any amendment or supplement to the
     Registration Statement, or (ii) the omission or alleged omission to state
     in the Registration Statement or any document incorporated by reference in
     the Registration Statement, a material fact required to be stated therein
     or necessary to make the statements therein in light of the circumstances
     under which they were made, not misleading; provided, that insofar as such
     losses, claims, damages, liabilities, costs and expenses are caused by any
     such untrue statement or omission or alleged untrue statement or omission
     of material fact so made in reliance upon and in conformity with
     information furnished in writing to the Company by the Purchasers or on the
     Purchasers' behalf expressly for inclusion therein; and provided, further,
     that the Company shall not be liable to any indemnified party to the extent
     that any such loss, claim, damage, liability cost or expense resulted from
     the fact that the Purchasers sold Shares to a person to whom the Purchasers
     failed to send or give a copy of the Prospectus or the Prospectus
     Supplement (an "Indemnifiable Matter").

     The indemnifying party will reimburse the indemnified party and each such
     controlling person promptly upon demand for any legal or other costs or
     expenses reasonably incurred by the indemnified party or the controlling
     person in investigating, defending against, or preparing to defend against
     any claim relating to the applicable Indemnifiable Matter.


(b)  INDEMNIFICATION BY PURCHASERS. The Purchasers agree to indemnify and hold
     -----------------------------
     harmless the Company, its officers, directors and agents and each person,
     if any, who controls the Company within the meaning of either Section 15 of
     the Securities Act or Section 20 of the Exchange Act to the same extent as
     the foregoing indemnity from the Company to the Purchasers, but only with
     respect to information furnished in writing by the Purchasers or with the
     Purchasers' authorization on the Purchasers' behalf expressly for use in





     any registration statement or prospectus relating to the Shares, or any
     amendment or supplement thereto.

(c)  INDEMNIFICATION PROCEDURES. Promptly after a person receives notice of a
     --------------------------
     claim or the commencement of an action, suit or proceeding for which the
     person intends to seek indemnification under Paragraph (a), the person will
     notify the indemnifying party in writing of the claim or commencement of
     the action, suit or proceeding, but failure to notify the indemnifying
     party will not relieve the indemnifying party from liability under
     Paragraph (a), except to the extent the indemnifying party has been
     materially prejudiced by the failure to give notice. The indemnifying party
     will be entitled to participate in the defense of any claim, action, suit
     or proceeding as to which indemnification is being sought, or the
     indemnifying party may (but will not be required to) assume the defense
     against the claim, action, suit or proceeding with legal counsel chosen by
     the indemnifying party. After an indemnifying party notifies an indemnified
     party that the indemnifying party wishes to assume the defense of a claim,
     action, suit or proceeding the indemnifying party will not be liable for
     any legal or other expenses incurred by the indemnified party in connection
     with the defense against the claim, action, suit or proceeding, except that
     if, in the opinion of legal counsel to the indemnifying party, one or more
     of the indemnified parties should be separately represented in connection
     with a claim, action, suit or proceeding the indemnifying party will pay
     the reasonable fees and expenses of one separate counsel for the
     indemnified parties. Each indemnified party, as a condition precedent to
     receiving indemnification as provided in Paragraph (a), will, at the cost
     and expense of the indemnifying party, cooperate in all reasonable respects
     with the indemnifying party in the defense of the claim, action, suit or
     proceeding as to which indemnification is sought. No indemnifying party
     will be liable for any settlement of any claim, action, suit or proceeding
     effected without its prior written consent. No indemnifying party will,
     without the prior written consent of the indemnified party, effect any
     settlement of a pending or threatened claim, action or proceeding with
     respect which an indemnified party is, or is informed that it may be, made
     a party and for which it would be entitled to indemnification, unless the
     settlement includes an unconditional release of the indemnified party from
     all liability and claims which are the subject matter of the pending or
     threatened action other than financial obligations for which the
     indemnified party will be indemnified hereunder.

(d)  CONTRIBUTION. If for any reason the indemnification provided for in this
     ------------
     Agreement is not available to, or is not sufficient to hold harmless, an
     indemnified party in respect of any loss, claim, damage, liability, cost or
     expense referred to in Paragraph (a), each indemnifying party will, in lieu
     of indemnifying the indemnified party, contribute to the amount paid or
     payable by the indemnified party, as a result of the loss, claim, damage,
     liability, cost or expense (i) in the proportion which is appropriate to
     reflect the relative benefits received by the indemnifying party, on the
     one hand, and by the indemnified party, on the other hand, from the sale of
     stock which is the subject of the claim, action, suit or proceeding which
     resulted in the loss, claim, liability, cost or expense or (ii) if that
     allocation is not permitted by applicable law, in such proportion as is
     appropriate to reflect not only the relative benefits of the sale of stock,
     but also the relative fault of the indemnifying party and the indemnified
     party with respect to the statements or omissions which are the subject of



                                       2


     the claim, action, suit or proceeding that resulted in the loss, claim,
     damage, liability, cost or expense as well as any other relevant equitable
     considerations.


                                       3