FORM 10-K

30

MDU RESOURCES G ROUP, INC.

DEFINITIONS

Lower Willamette Group

South Dakota Public Utilities Commission

LWG

SDPUC

Mid-Continent Area Power Pool

U.S. Securities and Exchange

MAPP

SEC

Commission

Thousands of barrels of oil or other

MBbls

liquid hydrocarbons

Securities Act Industry Guide 7 Description of Property by Issuers

Engaged or to be Engaged in Significant

Morse Bros., Inc., an indirect wholly

MBI

Mining Operations

owned subsidiary of Knife River

Supplemental Environmental Impact

SEIS

Thousand cubic feet

Mcf

Statement

Management's Discussion and Analysis

MD&A

Statement of Financial Accounting

SFAS

of Financial Condition and Results of

Standards

Operations

Accounting for the Effects of Certain

SFAS No. 71

Thousand decatherms

Mdk

Types of Regulation

MDU Brasil Ltda., an indirect wholly

MDU Brasil

Accounting for Income Taxes

SFAS No. 109

owned subsidiary of Centennial

International

Accounting for Certain Investments in

SFAS No. 115

Debt and Equity Securities

MDU Construction Services Group, Inc.,

MDU Construction Services

a direct wholly owned subsidiary of

Accounting for Stock-Based

SFAS No. 123

Centennial

Compensation

MDU Energy Capital, LLC, a direct wholly

Share-Based Payment (revised 2004)

MDU Energy Capital

SFAS No. 123 (revised)

owned subsidiary of the Company

Business Combinations (revised 2007)

SFAS No. 141 (revised)

Midwest Independent Transmission

Midwest ISO

Goodwill and Other Intangible Assets

SFAS No. 142

System Operator, Inc.

Accounting for Asset Retirement

SFAS No. 143

Million Btu

MMBtu

Obligations

Million cubic feet

MMcf

Accounting for the Impairment or

SFAS No. 144

Disposal of Long-Lived Assets

Million cubic feet equivalent

MMcfe

Million decatherms

Accounting for Stock-Based

MMdk

SFAS No. 148

Compensation -- Transition and Disclosure

Minnesota Public Utilities Commission

MNPUC

-- an amendment of SFAS No. 123

Montana-Dakota Utilities Co., a public

Montana-Dakota

Fair Value Measurements

SFAS No. 157

utility division of the Company

Employers' Accounting for

SFAS No. 158

Montana State Department of

Montana DEQ

Defined Benefit Pension and Other

Environmental Quality

Postretirement Plans

Montana Federal District Court U.S. District Court for the District

The Fair Value Option for Financial Assets

SFAS No. 159

of Montana

and Financial Liabilities

Indenture of Mortgage dated May 1,

Mortgage

Noncontrolling Interests in Consolidated

SFAS No. 160

1939, as supplemented, amended and

Financial Statements -- an amendment of

restated, from the Company to The Bank

ARB No. 51 (Consolidated Financial

of New York and Douglas J. MacInnes,

Statements)

successor trustees

A separate electric system owned by

Sheridan System

MPX Termoceara Ltda. (49 percent

MPX

Montana-Dakota

ownership, sold in June 2005)

Surface Mining Control and

SMCRA

Montana Public Service Commission

MTPSC

Reclamation Act

Megawatt

MW

Company's Dividend Reinvestment and

Stock Purchase Plan

North Dakota Department of Health

ND Health Department

Direct Stock Purchase Plan

North Dakota Public Service Commission

NDPSC

Termoceara Generating Facility 220-MW natural gas-fired electric

generating facility in the Brazilian state

National Environmental Policy Act

NEPA

of Ceara, owned and operated by MPX

National Historic Preservation Act

NHPA

(the Company's 49-percent ownership

interest was sold in June 2005)

U.S. Ninth Circuit Court of Appeals

Ninth Circuit

Tongue River Water Users' Association

TRWUA

Northern Plains Resource Council

NPRC

WBI Holdings, Inc., a direct wholly owned

WBI Holdings

Oregon Public Utilities Commission

OPUC

subsidiary of Centennial

Order on Rehearing and Compliance and

Order on Rehearing

Westmoreland Coal Company

Westmoreland

Remanding Certain Issues for Hearing

Williston Basin Interstate Pipeline

Williston Basin

Oregon State Department of

Oregon DEQ

Company, an indirect wholly owned

Environmental Quality

subsidiary of WBI Holdings

Polychlorinated biphenyls

PCBs

Washington Utilities and Transportation

WUTC

Power purchase and sale agreement

PPA

Commission

Prairielands Energy Marketing, Inc.,

Prairielands

Wyoming State Department of

Wyoming DEQ

an indirect wholly owned subsidiary of

Environmental Quality

WBI Holdings

Wyoming Federal District Court U.S. District Court for the District

Company's 2008 Proxy Statement

Proxy Statement

of Wyoming

Prevention of Significant Deterioration

PSD

Wyoming Public Service Commission

WYPSC

Resource Conservation and Recovery Act

RCRA