The team announced the deal Thursday. Resop joined the AL West champion A's in a Nov. 30 trade with Pittsburgh, sending minor league right-hander Zach Thornton to the Pirates. Resop went 1-4 with one save and a 3.91 ERA in 61 relief appearances with Pittsburgh last year.
He worked a career-high 73 2-3 innings, tied for seventh among National League relievers. The 30-year-old Resop allowed a .276 opponents batting average, including .237 against left-handed hitters.