After the 1987 season, Cincinnati traded Parker to the Oakland Athletics for José Rijo and Tim Birtsas. In Oakland, Parker was able to extend his career by spending most of his time as a designated hitter. Although injuries and age caught up to him to a degree – he hit just .257 with 12 homers in 377 at-bats in 1988 and .264 with 22 homers in 553 at-bats in 1989 – his veteran leadership was a significant factor in the A's consecutive World Series appearances.