INSTRUMENT OF AMENDMENT TO THE
MDU RESOURCES GROUP, INC.
401(k) RETIREMENT PLAN

The MDU Resources Group, Inc. 401(k) Retirement Plan (as amended and restated
March 1, 2011) (the “Plan”), is hereby further amended, effective as of July 1,
2012, unless otherwise indicated, as follows:

1.
Effective as of May 1, 2012, by adding WBI Energy, Inc. (“WBIE”) as a
Participating Affiliate and to the table in Section D‑1‑2 Eligibility to Share
in the Profit Sharing Feature of Supplement D-1, Provisions Relating to the
Profit Sharing Feature for Certain Participating Affiliates.

Explanation: This amends Supplement D-1 to reflect WBIE as a Participating
Affiliate due to WBI’s restructuring.

2.
By removing WBI Holdings, Inc. (“WBIH”) as a Participating Affiliate and from
the table in Section D‑1‑2 Eligibility to Share in the Profit Sharing Feature of
Supplement D-1, Provisions Relating to the Profit Sharing Feature for Certain
Participating Affiliates.

Explanation: This amends Supplement D-1 as employees of WBIH became employees of
WBIE on July 1, 2012, due to WBI’s restructuring. WBIH is removed as a
Participating Affiliate as the Company no longer has employees.

3.
By further modifying the table and footnotes in Section D‑1‑2 Eligibility to
Share in the Profit Sharing Feature of Supplement D-1, Provisions Relating to
the Profit Sharing Feature for Certain Participating Affiliates to reflect the
name changes of Bitter Creek Pipelines, LLC and its division Total Corrosion
Solutions to WBI Energy Midstream, LLC and WBI Energy Corrosion Services,
respectively; and Williston Basin Interstate Pipeline Company to WBI Energy
Transmission, Inc.

Explanation: This reflects the name changes of Bitter Creek Pipelines, LLC, its
division Total Corrosion Solutions, and Williston Basin Interstate Pipeline
Company as Participating Affiliates and amends Supplement D-1, effective as of
July 1, 2012.

4.
By modifying the table and footnote in Section D‑2‑2 Eligibility to Share in the
Retirement Contribution of Supplement D-2, Provisions Relating to the Retirement
Contribution Feature for Certain Participating Affiliates to reflect the name
change of Bitter Creek Pipelines, LLC to WBI Energy Midstream, LLC.

Explanation: This amends Supplement D-2 to reflect the name change of Bitter
Creek Pipelines, LLC as a Participating Affiliate, effective as of July 1, 2012.

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5.
By removing Knife River – Western North Dakota Division, a Division of Knife
River Corporation – North Central (“KR-WND”) as a Participating Affiliate and
from the table in Section D-3-2 Eligibility to Share in the Profit Sharing
Feature of Supplement D-3, Provisions Relating to the Profit Sharing Feature for
Certain Participating Affiliates.

Explanation: This amends the Participating Affiliates in the table of Supplement
D-3 to reflect the consolidation of the two North Dakota divisions of Knife
River Corporation – North Central.

6.
By adding the following paragraph to the end of Section D-3-3 Amount of Profit
Sharing Contributions, Allocation of Supplement D-3, Provisions Relating to the
Profit Sharing Feature for Certain Participating Affiliates:

Notwithstanding the foregoing, for the Plan Year ended December 31, 2012,
eligible employees of KR-WND as of June 30, 2012, shall receive profit sharing
contributions in an amount equal to the greater of: (i) the profit sharing
contributions determined using consolidated profitability measures; or (ii) the
profit sharing contributions determined using separate profitability measures.

Explanation: This amends Supplement D-3 to ensure that the profit sharing
contribution for eligible employees of KR-WND are not less than what they would
have been entitled to receive had the consolidation not occurred during the
middle of the Plan Year.

7.
By adding WBIE as a Participating Affiliate, removing WBIH as a Participating
Affiliate, and changing Williston Basin Interstate Pipeline Company to WBI
Energy Transmission, Inc. in Section D‑6‑2 Eligibility to Share in the
Retirement Contribution of Supplement D-6, Provisions Relating to the MDU Group
Inc. Retirement Contribution Feature.

Explanation: This amends Supplement D-6 to reflect WBIE as a Participating
Affiliate, as the result of moving the employees of WBIH to WBIE, and the name
change for Williston Basin Interstate Pipeline Company. WBIH is removed as a
Participating Affiliate as the Company no longer has employees.

8.
By replacing the following entry in Schedule B, in its entirety:

Knife River – Western North Dakota Division (KR-WND), a division of Knife River
Corporation – North Central shall make supplemental contributions on behalf of
its Davis-Bacon Employees in such amounts as may be necessary to satisfy the
Prevailing Wage Law’s required fringe cost to the extent that the sum of the
employer Matching and Profit

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Sharing Contributions, if any, for a period are insufficient to satisfy the
Prevailing Wage Law’s required fringe cost pursuant to Supplement G; however,
effective as of July 1, 2012, KR‑WND shall no longer be a Participating
Affiliate under the terms of the Plan and correspondingly shall not make Davis
Bacon contributions for any pay period beginning on or after July 1, 2012.

Effective March 17, 2011 and as amended as of July 1, 2012.

Explanation: This amends Schedule B to reflect that KR-WND is no longer a
Participating Affiliate, effective as of July 1, 2012.

IN WITNESS WHEREOF, MDU Resources Group, Inc., as Sponsoring Employer of the
Plan, has caused this Supplement to be duly executed by a member of the MDU
Resources Group, Inc. Employee Benefits Committee on this 29th day of August,
2012.

 
MDU RESOURCES GROUP, INC.
 
EMPLOYEE BENEFITS COMMITTEE
 
 
 
 
 
 
 
By:
/s/ Doran N. Schwartz
 
 
Doran N. Schwartz, Chairman

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