FORM 10-K

29

MDU RESOURCES G ROUP, INC.

DEFINITIONS

MDU Resources Group, Inc.

Company

The following abbreviations and acronyms used in this Form 10-K are

defined below:

U.S. Court of Appeals for the District of

D.C. Appeals Court

Columbia Circuit

Abbreviation or Acronym

Decatherm

dk

Allowance for funds used during

AFUDC

construction

Dakota Resource Council

DRC

Administrative Law Judge

ALJ

Elk Basin Storage Reservoir, one of

EBSR

Williston Basin's natural gas storage

Tecnica de Engenharia Electrica -- Alusa

Alusa

reservoirs, which is located in Montana

Anadarko Petroleum Corporation

Anadarko

and Wyoming

Accounting Principles Board

APB

Empresa Catarinense de Transmissão de

ECTE

Energia S.A.

Accounting for Stock-Based Compensation

APB Opinion No. 25

Environmental Impact Statement

EIS

U.S. Army Corps of Engineers

Army Corps

Emerging Issues Task Force

EITF

Tongue River-Badger Hills Project

Badger Hills Project

Revenue Arrangements with Multiple

EITF No. 00-21

Barrel of oil or other liquid hydrocarbons

Bbl

Deliverables

Billion cubic feet

Bcf

Revenue Recognition of Long-Term Power

EITF No. 91-6

Montana Board of Environmental Review

BER

Sales Contracts

450-MW coal-fired electric generating

Big Stone Station

Empresa Norte de Transmissão de

ENTE

facility located near Big Stone City,

Energia S.A.

South Dakota (22.7 percent ownership)

U.S. Environmental Protection Agency

EPA

Proposed coal-fired electric generating

Big Stone Station II

Empresa Regional de Transmissão de

ERTE

facility located near Big Stone City,

Energia S.A.

South Dakota (the Company anticipates

ownership of at least 116 MW)

Endangered Species Act

ESA

Bitter Creek Pipelines, LLC, an indirect

Bitter Creek

Securities Exchange Act of 1934,

Exchange Act

wholly owned subsidiary of WBI Holdings

as amended

Black Hills Power and Light Company

Black Hills Power

Financial Accounting Standards Board

FASB

Bureau of Land Management

BLM

Federal Energy Regulatory Commission

FERC

Brascan Brasil Ltda.

Brascan

Fidelity Exploration & Production

Fidelity

Company, a direct wholly owned

Company's equity method investment in

Brazilian Transmission Lines

subsidiary of WBI Holdings

companies owning ECTE, ENTE and ERTE

FASB Interpretation No.

FIN

British thermal unit

Btu

Accounting for Conditional Asset

FIN 47

Carib Power Management LLC

Carib Power

Retirement Obligations - An Interpretation

Cascade Natural Gas Corporation, an

Cascade

of FASB Statement No. 143

indirect wholly owned subsidiary of MDU

Accounting for Uncertainty in

FIN 48

Energy Capital (acquired July 2, 2007)

Income Taxes

Coalbed natural gas

CBNG

Great Plains Natural Gas Co., a public

Great Plains

Centrais Elétricas de Santa Catarina S.A.

CELESC

utility division of the Company

Colorado Energy Management, LLC, a

CEM

Hartwell Energy Limited Partnership,

Hartwell

former direct wholly owned subsidiary of

a former equity method investment

Centennial Resources (sold in the third

of the Company (sold in the third quarter

quarter of 2007)

of 2007)

Companhia Energética de Minas Gerais

CEMIG

Howell Petroleum Corporation, a wholly

Howell

owned subsidiary of Anadarko

Centennial Energy Holdings, Inc., a direct

Centennial

wholly owned subsidiary of the Company

International Brotherhood of

IBEW

Electrical Workers

Centennial Holdings Capital LLC, a direct

Centennial Capital

wholly owned subsidiary of Centennial

International Chemical Workers Union

ICWU

Centennial Energy Resources

Centennial International

Indenture dated as of December 15, 2003,

Indenture

International, Inc., a direct wholly owned

as supplemented, from the Company to

subsidiary of Centennial Resources

The Bank of New York as Trustee

Centennial Power, Inc., a former

Centennial Power

Innovatum, Inc., a former indirect

Innovatum

direct wholly owned subsidiary of

wholly owned subsidiary of WBI Holdings

Centennial Resources (sold in the third

(the stock and Innovatum's assets have

quarter of 2007)

been sold)

Centennial Energy Resources LLC, a direct

Centennial Resources

Financial Statements and

Item 8

wholly owned subsidiary of Centennial

Supplementary Data

Comprehensive Environmental Response,

CERCLA

Kennecott Coal Sales Company

Kennecott

Compensation and Liability Act

Knife River Corporation, a direct wholly

Knife River

Federal Clean Air Act

Clean Air Act

owned subsidiary of Centennial

Federal Clean Water Act

Clean Water Act

Company's 401(k) Retirement Plan

K-Plan

Cost Management Services, Inc.

CMS

Kilowatts

kW

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

Kilowatt-hour

kWh

of Colorado