UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 10-K/A (Amendment No. 1) [X] ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2006 OR [ ] TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from _____________ to ______________ Commission file number 1-3480 MDU Resources Group, Inc. (Exact name of registrant as specified in its charter) Delaware 41-0423660 (State or other jurisdiction of (I.R.S. Employer incorporation or organization) Identification No.) 1200 West Century Avenue P.O. Box 5650 Bismarck, North Dakota 58506-5650 (Address of principal executive offices) (Zip Code) (701) 530-1000 (Registrant's telephone number, including area code) Securities registered pursuant to Section 12(b) of the Act: Name of each exchange Title of each class on which registered ------------------- ------------------- Common Stock, par value $1.00 New York Stock Exchange and Preference Share Purchase Rights Securities registered pursuant to Section 12(g) of the Act: Preferred Stock, par value $100 ------------------------------- (Title of Class) Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes |X| No | | Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Exchange Act. Yes | | No |X| Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes |X| No | | Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of the registrant's knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. |X| Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, or a non-accelerated filer. See definition of "accelerated filer and large accelerated filer" in Rule 12b-2 of the Exchange Act (Check one): Large accelerated filer |X| Accelerated filer | | Non-accelerated filer | | Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). Yes | | No |X| State the aggregate market value of the voting common stock held by nonaffiliates of the registrant as of June 30, 2006: $4,393,239,107. Indicate the number of shares outstanding of each of the registrant's classes of common stock, as of February 12, 2007: 181,147,966 shares. DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant's 2007 Proxy Statement are incorporated by reference in Part III, Items 10, 11, 12, 13 and 14 of this Report. Explanatory Note The information contained in Items 10, 11 and 13 in the Annual Report on Form 10-K filed on February 21, 2007 did not incorporate by reference all required information from the Company's 2007 Proxy Statement. PART III ITEM 10. DIRECTORS, EXECUTIVE OFFICERS AND CORPORATE GOVERNANCE The information required by this item is included under the captions "Item 1. Election of Directors," "Continuing Incumbent Directors," "Information Concerning Executive Officers," the first and third paragraphs under "Corporate Governance - Audit Committee," "Corporate Governance - Code of Conduct" and "Section 16(a) Beneficial Ownership Reporting Compliance" in the Proxy Statement, which information is incorporated herein by reference. ITEM 11. EXECUTIVE COMPENSATION The information required by this item is included under the caption "Executive Compensation" in the Proxy Statement, which information is incorporated herein by reference. ITEM 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS, AND DIRECTOR INDEPENDENCE The information required by this item is included under the captions "Related Person Disclosure" and "Corporate Governance - Director Independence" in the Proxy Statement, which information is incorporated herein by reference. PART IV ITEM 15. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES (a) FINANCIAL STATEMENTS, FINANCIAL STATEMENT SCHEDULES AND EXHIBITS 3. Exhibits Exhibits filed herewith: 31(a) Certification of Chief Executive Officer filed pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 31(b) Certification of Chief Financial Officer filed pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 1 32 Certification of Chief Executive Officer and Chief Financial Officer furnished pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 2 SIGNATURES Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this amendment to be signed on its behalf by the undersigned, thereunto duly authorized. MDU RESOURCES GROUP, INC. Date: March 1, 2007 By: /s/ Vernon A. Raile ------------------- Vernon A. Raile Executive Vice President, Treasurer and Chief Financial Officer 3 EXHIBIT INDEX Exhibit Number Description of Exhibit 31(a) Certification of Chief Executive Officer filed pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 31(b) Certification of Chief Financial Officer filed pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 32 Certification of Chief Executive Officer and Chief Financial Officer furnished pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002