Olson, the A's No. 1 prospect as ranked by MLB.com, was selected for the U.S. roster, while the Venezuelan-born Nunez, the A's No. 4 prospect, was named to the World Team.
Olson, 21, is batting .212 with eight home runs and 34 RBIs through 71 games for Double-A Midland but still boasts a .374 on-base percentage, having drawn 65 walks.
Nunez has nine home runs for the RockHounds, despite having played in just 47 games after starting the year on the disabled list. The 21-year-old corner infielder is batting .238 overall.
Major League Baseball, in conjunction with the Major League Baseball Scouting Bureau, MLB.