Shares of Atlas Corp. /zigman2/quotes/206592404/composite ATCO -0.07% jumped nearly 8% in premarket trades on Monday after a buyout group including Atlas Corp. chairman David L. Sokol increased its take-private offer for the container ship and mobile power company to $15.50 a share, up from its Aug. 4 offer of $14.45 a share. Poseidon Acquisition Corp., on behalf of a consortium made up of Sokol, Fairfax Financial Holdings Ltd. /zigman2/quotes/207415723/delayed CA:FFH -0.66% , the Washington Family, and Ocean Network Express Pte. Ltd. said the price of $15.50 a share represents Poseidon's final and best offer. Poseidon made the offer in a letter to a special committee of the Atlas board of directors. Atlas Corp. shares closed at $13.52 a share on Friday, with a market capitalization of $3 billion.