The A's added outfield depth Tuesday by acquiring Gentry along with right-hander Josh Lindblom from the division rival Texas Rangers for outfielder Michael Choice and minor league infielder Chris Bostick.
The teams announced the deal Tuesday, a day after Oakland traded for AL saves leader Jim Johnson in a swap with Baltimore and also reached agreement on a $22 million, two-year contract with left-handed starter Scott Kazmir.
"I definitely didn't anticipate it, it caught me off guard a little bit," Gentry said. "Being on the other side of the white lines from these guys so many years, it's a great ballclub."
While the two-time defending AL West champion A's have their starting outfield returning in center fielder Coco Crisp, left fielder Yoenis Cespedes and right fielder Josh Reddick, Gentry provides an option off the bench and creates depth. The returnees have dealt with injuries in recent seasons.
Gentry said he is comfortable playing all three outfield spots.
"I really don't know what my role is going to be," said Gentry, who had yet to speak to the A's brass. "Hopefully whatever I can to help the team keep winning and keep up their streak. They handle themselves, they play hard. That team is exactly the type of player I am. I think I'm going to fit in well over there."
Gentry batted .280 with two homers and 22 RBIs in 106 games for the Rangers this year, while Lindblom went 1-3 with a 5.46 ERA in five starts and three relief appearances over three stints with the Rangers this year.
Gentry received a call from Rangers general manager Jon Daniels while on the golf course Tuesday with news of the trade.
"It's a big rivalry between Oakland and Texas," Gentry said of his success against the A's.
For the Rangers, acquiring Choice brings the outfielder back home to Texas and he will have a chance to contribute right away rather than be competing to make the big league team out of spring training with Oakland.
"It's something I've always dreamed about, playing at home," said Choice, a Fort Worth native who grew up attending Rangers games while going to high school and college in Arlington.
The 24-year-old Choice, taken by Oakland with the 10th overall pick in the 2010 amateur draft, made his major league debut in September and played nine games late in the season for the A's, batting .278 with a double and two runs scored.
Daniels considers Choice an option for now and the future. Choice could become the everyday left fielder if the Rangers don't re-sign Nelson Cruz.
Bostick played for Class A Beloit in 2013 and hit .282 with 14 home runs and 89 RBIs in 129 games. He drew 51 walks for a .354 on-base percentage and stole 25 bases. He provides depth for the organization in the middle infield.
AP Sports Writer Stephen Hawkins contributed to this report.