Unhappy in Milwaukee, Conigliaro announced his retirement from baseball in the middle of the 1972 season. He applied for reinstatement in 1973, and the Brewers sold Conigliaro to the Oakland Athletics for an undisclosed amount of money. He appeared with the Athletics in that season's American League Championship Series and the World Series, where he was hitless in seven at bats. He had knee surgery during the offseason, and was waived by Oakland in March 1974. He attempted a comeback with the Athletics in 1977, but declined an assignment to the minor leagues. He finished his career with a .256 batting average, 40 home runs, and 128 RBIs in 347 games played.