18-21 games each year. He was fine in the postseason too, going 6-4 with a 2.30 ERA.
And lastly, I can't help but mention Bobby Shantz (1949-56). He is perhaps known by many as a reliever for the Yankees for a few years late in this career, but he actually pitched for the Athletics franchise from 1949-56, and mostly as a starter. In 1951 he was 18-10, but in 1952 he had a career year going 24-7 with a 2.48 ERA, completing 27 of his 33 starts. He led the league in both wins and ERA that year, which was enough to earn him the AL MVP Award.
Dennis Eckersley (1987-95) started his career as a starter for the Indians, Red Sox and Cubs, and had some success in that role. But when he joined the A's in 1987, manager Tony LaRussa used him as a closer as Jay Howell was faltering in that role. For the next five seasons he was as unhittable as almost any pitcher has ever been. He racked up SV totals of 45, 33, 48, 43, and 51. His pinpoint control led to some insanely good numbers. In 1989 he pitched 57.7 innings, struckout 55 but walked only 3. Then in 1990 he had a microscopic 0.60 ERA over 73.3 innings, while striking out 73 and only walking 4. He regularly earned consideration for both the Cy Young and MVP awards, and in 1992 finally took home both based on a 7-1 record, 51 SV, and a 1.91 ERA. He had some issues in the postseason -- including allowing the famous one- legged HR to Kirk Gibson in 1988. But he clearly has earned the top spot relief spot on this roster.
This means that Rollie Fingers (1968-76) is bumped to the number two spot. He pitched the first half of his career for Oakland, and the first few years were mixed as a starter and reliever. He took over closer duties in 1972 and had five consecutive seasons of 18-24 SV and ERA below 3.00. He was generally solid in the postseason too, saving 8 games with a 2.22 ERA.
As I indicated earlier, the other reliever candidates didn't impress me much, so none are being selected for this all-time team. In reverse chronological order, Huston Street (2005-08) burst onto the scene in 2005 with 23 saves and a 1.72 ERA. He followed that up with 37 saves, but then only pitched two more seasons with the A’s before heading to Colorado. Billy Taylor (1994-99) was the closer for four seasons in the late 1990s, with 1998 being his best year with 33 SV and a 3.58 ERA. And going way back, John Wyatt (1961-66, 69) was a respectable late-innings reliever for the Kansas City A's for several years. He posted 20+ SV twice, during an era when this was not as common as today.