EXHIBIT 11.1 AMERICAN MOBILE SATELLITE CORPORATION --------------------------------------- COMPUTATIONS OF EARNINGS PER COMMON SHARE --------------------------------------- (in thousands, except per share amounts) --------------------------------------- Three Months Ended June 30, Six Months Ended June 30, 1999 1998 1999 1998 ---- ---- ---- ---- BASIC EARNINGS PER SHARE CALCULATION Net Loss ($42,377) ($42,989) ($85,520) ($70,395) ========= ========= ========= ========= Net Loss per common share ($1.31) ($1.36) ($2.65) ($2.47) ======= ======= ======= ======= Weighted-average common shares 32,416 31,719 32,321 28,502 ====== ====== ====== ====== outstanding DILUTED EARNINGS PER SHARE CALCULATION Net Loss ($42,377) ($42,989) ($85,520) ($70,395) ========= ========= ========= ========= Net Loss per common share ($1.16) ($1.34) ($2.28) ($2.46) ======= ======= ======= ======= Weighted-average common shares (1) 36,668 32,102 37,500 28,613 ====== ====== ====== ====== (1) Calculated as follows: Historical weighted average number of shares outstanding 32,416 31,719 32,321 28,502 Assumed exercise of stock options 1,364 -- 1,297 -- Assumed exercise of stock purchase warrants 2,888 383 3,882 111 ----- ------ ----- --- 36,668 32,102 37,500 28,613 ====== ====== ====== ======