EXHIBIT 15 DELOITTE & TOUCHE - ---------------------------------------------------------------- 3900 US Bancorp Tower Telephone: (503) 222-1341 111 SW Fifth Avenue Facsimile: (503) 224-2172 Portland, Oregon 97204-3698 April 28, 1994 Northwest Natural Gas Company 220 N.W. Second Avenue Portland, Oregon 97209 We have made a review, in accordance with standards established by the American Institute of Certified Public Accountants, of the unaudited interim financial information of Northwest Natural Gas Company and subsidiaries for the periods ended March 31, 1994 and 1993, as indicated in our report dated April 28, 1994; because we did not perform an audit, we expressed no opinion on that information. We are aware that our report referred to above, which is included in your quarterly report on Form 10-Q for the quarter ended March 31, 1994, is incorporated by reference in Registration Statement No. 33-34724, Post-Effective Amendment No. 1 to Registration Statement No. 2-76276, and Post-Effective Amendments No. 2 to Registration Statement Nos. 2-77195 and 33-19354 on Form S-8 and in Registration Statement Nos. 33-44827, 33-64014, and 33-51271, and Post-Effective Amendments No. 1 to Registration Statement Nos. 33-1304 and 33-20384 on Form S-3. We also are aware that the aforementioned report, pursuant to Rule 436(c) under the Securities Act, is not considered a part of the Registration Statement prepared or certified by an accountant or a report prepared or certified by an accountant within the meaning of Sections 7 and 11 of that Act. /s/ Deloitte & Touche DELOITTE & TOUCHE