Wells was previously designated by the Mariners on the last day of Spring Training. He was claimed off waivers by the Blue Jays on April 10 and never appeared in a game with them before again being designated five days later.
Oakland acquired his services for outfield depth while Yoenis Cespedes was stationed on the disabled list, but there was simply no room for him on the roster once Cespedes returned Sunday.
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.