Exhibit (11) NORTHWEST NATURAL GAS COMPANY Statement Re: Computation of Per Share Earnings (Thousands, except per share amounts) (Unaudited) 12 Months Ended December 31 --------------------------------- 1997 1996 1995 ---- ---- ---- Earnings Applicable to Common Stock $40,413 $44,070 $35,259 Debenture Interest Less Taxes 455 479 528 ------- ------- ------- Earnings Applicable to Diluted Common Stock $40,868 $44,549 $35,787 ======= ======= ======= Average Common Shares Outstanding 22,698 22,391 21,817 Stock Options 32 27 11 Convertible Debentures 518 545 600 ------ ------ ------ Diluted Average Common Shares Outstanding 23,248 22,963 22,428 ====== ====== ====== Diluted Earnings Per Share of Common Stock $1.76 $1.94 $1.60 ===== ===== ===== Note: Primary earnings per share are computed on the weighted daily average number of common shares outstanding each year. Outstanding stock options are common stock equivalents but are excluded from primary earnings per share computations due to immateriality.