Moore, outrighted by the Astros earlier this month, played in 72 games for Houston this year, splitting time at third base, first base, right field, second base and left field.
"I had quite a few offers and Oakland called me and talked to me and basically there, guys in my situation have been known to get pretty good opportunities to play," Moore said. "Also, I'm going into my 12th season and I've never really anywhere remotely close to home (Southern California) and that was pretty exciting, too."
Moore, 29, is a career .242 hitter with 16 home runs and 53 RBIs in 152 games. Aside from the Astros, he has also spent time with the Cubs and Orioles.