Exhibit 16 February 20, 2002 Office of the Chief Accountant Securities and Exchange Commission 450 Fifth Street, N.W. Washington, D.C. 20549 Dear Sir/Madam: We have read Item 4 included in the Form 8-K dated February 20, 2002 of MDU Resources Group, Inc. filed with the Securities and Exchange Commission and are in agreement with the statements contained therein. Very truly yours, /s/ Arthur Andersen LLP Arthur Andersen LLP cc: Warren L. Robinson, Executive Vice President, Treasurer and Chief Financial Officer, MDU Resources Group, Inc.