Jeurys Familia has a 2.88 ERA in 40 appearances this season.
New York will end up with two prospects and international slot money.
The 28-year-old right-hander has a 2.88 ERA and 43 strikeouts in 40 2/3 innings for New York this season. With the Mets at the bottom of the NL East currently, they are looking to sell and are also reportedly looking to get back elite prospects for pitchers Jacob deGrom and Noah Syndergaard.
Oakland entered Saturday third in the AL West at 55-43, nine games behind the Astros for first in the division and three games behind the Mariners for the second Wild Card spot.
Closer Blake Treinen has held down the back of Oakland's bullpen this season, posting 24 saves, a 0.94 ERA and 61 strikeouts in 48 innings of work prior to the All-Star break. It is likely he will remain in that position, and Familia will add depth to the rest of the bullpen.
In 2016 Familia was named an All-Star, posted a 2.55 ERA and led MLB in saves with 51. For his career, Familia has a 2.66 ERA and 123 saves.