Oliver was signed by the Pirates as an amateur free agent in . He was promoted to the Major Leagues on September 14, 1968, which was the day his father, Al Oliver Sr., died. He appeared in 4 games that season. In his official rookie season, Oliver batted .285 with 17 home runs and drove in 70 runs, placing second in the National League Rookie of the Year voting. The following season, 1970, Oliver hit .270 and was fifth in the NL with seven sacrifice flies. He also finished second in the league with the 14 times he was hit by a pitch (the previous year he was plunked 12 times, fourth in the league). The Pirates won the National League East title for their first trip to the postseason since winning the 1960 World Series. However, they lost to the Cincinnati Reds in the 1970 National League Championship Series.