Multiple teams are still involved in recruiting the right-hander, with a deal expected to be finalized during the winter meetings which kick off on Monday in San Diego.
Romo authored a 3.43 ERA and 3.68 FIP over 60 1/3 innings in 2019, splitting time between the Miami Marlins and Minnesota Twins. Over the past two seasons, the 36-year-old has collected 45 saves over 138 appearances with the Marlins, Twins, and Tampa Bay Rays.
The A's boasted one of baseball's best bullpens last year, ranking fourth by FanGraphs WAR with a collective 3.89 ERA and 3.98 FIP. The club recently non-tendered former closer Blake Treinen and left-hander Ryan Buchter, making the pair of relievers free agents.