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 “K-Plan”), is hereby further amended, as follows:

In addition, each Eligible Employee who did not have a Savings Contribution election of at least three percent (3%) of Compensation on file as of May 25, 2007,

shall be deemed to have elected to have three percent (3%) of Compensation withheld and contributed to the Plan as Savings Contributions effective as of the first payroll period beginning after the Effective Date, unless prior to August 21, 2007, such Eligible Employee has made an alternate election.

On February 7, 2013, MDU Resources Group, Inc., through its wholly-owned subsidiary, WBI Energy, Inc., (“WBI Energy”) formed Dakota Prairie Refining, LLC (“Dakota Prairie”). WBI Energy owns 50% of the membership interests of Dakota Prairie and Calumet North Dakota, LLC (“Calumet”) owns 50% of the membership interests of Dakota Prairie. Calumet and consequently Dakota Prairie are not members of the MDU Resources Group, Inc. controlled group of corporations within the meaning of Section 414(b) of the Code. Effective September 9, 2013, Dakota Prairie adopted the Plan for its eligible employees. Thereafter, with respect to Dakota Prairie, the Plan is maintained as a multiple employer plan (as defined in Section 413(c) of the Code) in

accordance with Supplement I. On June 28, 2016, Dakota Prairie was sold. Effective January 1, 2017, the Plan shall revert to and be maintained as a single employer plan.

I-6 Reversion to Single Employer Plan. Dakota Prairie was sold on June 28, 2016. As a result of this sale, Dakota Prairie is no longer a Participating Affiliate in the Plan. Therefore, effective January 1, 2017, this Supplement I is no longer applicable.

Eligibility to Share in the Profit Sharing Feature. Participation in the Profit Sharing Feature(s) for any Plan Year is limited to employees of the Supplement D-1 Company who satisfy the Plan’s definition of Eligible Employee (unless otherwise noted below). The current and original effective dates for each Participating Affiliate’s respective Profit Sharing Feature are listed below.

^1/Eligible employees only include those in salary grade levels 29-38.

^2/In the event a Participating Affiliate adopts a Profit Sharing Feature on a date other than January 1, effective as of the date of participation in the Plan, the amount of any such contribution allocated to a Supplement D‑1 Participant shall be based upon Compensation, received while in the employ of the Participating Affiliate after the date of acquisition by the Company or any Affiliate.

^3/Requirement to be an Active Employee on the last day of the Plan Year does not apply.

^4/The following participant of Kent’s Oil Service is granted vesting service for prior years of service with Spirit Road Oils: Jose Padilla.

^5/Eligible JTL Casper hourly employees (both union and nonunion), including those employees who participate in the Operating Engineers Local No. 800 & The Wyoming Contractors’ Association, Inc. Pension Trust Fund for Wyoming (JTL MEP employees.)

^6/Eligible salaried employees of JTL hired after December 31, 2014 or any other JTL employee who transfers to a salaried position after December 31, 2014.

^7/Eligible employees participating in a management incentive compensation plan are not eligible for a Profit Sharing Contribution.

In order to share in the allocation of any profit sharing contribution made by a Supplement D-1 Company pursuant to Paragraph 3 below for a given Plan Year, Participants employed by a Supplement D-1 Company must be credited with 1,000 Hours of Service (prorated for the Plan Year in which the Profit Sharing Feature becomes effective) in that Plan Year, be an Active Employee of the Supplement D-1 Company on the last day of the Plan Year, and must not be covered by a collectively bargained unit to which the Profit Sharing has not been extended.

However, an Eligible Employee of a Knife River Corporation Participating Affiliate who transfers during the Plan Year and remains employed by a Knife River Corporation Participating Affiliate on the last day of the Plan Year will be eligible to receive a prorated profit sharing contribution from each Knife River Corporation Participating

Affiliate.

Moreover, effective January 1, 2009, an Eligible Employee of Montana‑Dakota Utilities Co., Great Plains Natural Gas Co., Intermountain Gas Company, or Cascade Natural Gas Corporation (collectively the “Utility Group Participating Affiliate”) who transfers during the Plan Year and remains employed by a Utility Group Participating Affiliate on the last day of the Plan Year will be eligible to receive a prorated profit sharing contribution from each Utility Group Participating Affiliate noted above which meets its independent profitability targets.

Effective January 1, 2014, it was resolved that Profit Sharing contributions for Eligible Employees of the Utility Group Participating Affiliates would be based upon the Utility Group Participating Affiliates combined profitability targets, and therefore, if the Utility Group Participating Affiliates together attained the required profitability, Eligible Employees of the Utility Group Participating Affiliates would receive a contribution as long as they remained employed by a Utility Group Participating Affiliate on the last day of the Plan Year.

Notwithstanding the foregoing and except as noted herein, effective January 1, 2017, MDU Resources Group, Inc., Montana-Dakota Utilities Co., Intermountain Gas Company, Cascade Natural Gas Corporation, Great Plains Natural Gas Co., WBI Energy, Inc., WBI Energy Midstream, LLC, and WBI Energy Transmission, Inc. (collectively the “Regulated Group Participating Affiliates”) will provide a Profit Sharing contribution to Eligible Employees who are classified in salary grade levels 29‑38, or a prorated Profit Sharing contribution to Eligible Employees who transfer in or out of salary grade levels 29-38, provided the profitability target is met and they remain employed by a Regulated Group Participating Affiliate as of the last day of the Plan Year. Profit Sharing contributions for Eligible Employees of MDU Resources Group, Inc. will be based on an independent earnings per share target. Profit sharing contributions for Eligible Employees of WBI Energy, Inc., WBI Energy Midstream, LLC, and WBI Energy Transmission, Inc. will be based on a combined profitability target. Employees of the WBI Energy Corrosion Services division of WBI Energy Midstream, LLC are not eligible to receive Profit Sharing contributions. Profit Sharing contributions for Eligible Employees of the Utility Group Participating Affiliates (other than union employees of Montana-Dakota Utilities Co.) will be based on the Utility Group Participating Affiliates combined profitability targets. Profit Sharing contributions for union Eligible Employees of Montana‑Dakota Utilities Co., regardless of salary grade level, shall be determined based solely on the profitability of Montana‑Dakota Utilities Co.

For purposes of this Supplement, an “Active Employee” means an employee who is still on the payroll, has been temporarily laid off, or who terminated employment due to Disability, death, or after attaining age 60 during such Plan Year, but does not mean an employee whose employment has been terminated effective on or before December 31 of that Plan Year. In addition, for purposes of applying the requirement of completing 1,000 Hours of Service for the Plan Year, such requirement shall not apply to employees terminating after attaining age 60 provided they are not terminated for cause.

Participants who meet the preceding requirements are referred to herein as “Supplement D-1 Participant.”

IN WITNESS WHEREOF, MDU Resources Group, Inc., as Sponsoring Employer of the K-Plan, has caused this amendment to be duly executed by a member of the MDU Resources Group, Inc. Employee Benefits Committee on this 29th day of December, 2016.

Doran N. Schwartz, Chairman