dull was called up to the majors for the first time on september 1, 2015, and made his major league debut that night, pitching one inning of relief against the los angeles angels of anaheim. dull finished the 2015 season with 13 appearances, compiling a 1-2 record and 4.24 era. in 2016, dull began the season in oakland's bullpen and was a mainstay, appearing in 70 games while going 5-5 with a 2.42 era. in 2017, dull was placed on the disabled list at the end of may due to a right knee strain, and he did not return until late july. in 49 relief appearances for oakland, he was 2-2 with a 5.14 era. dull began 2018 with oakland, but was optioned to nashville in may. he pitched most of the season in aaa, appearing in 28 games for oakland.