Smith has spent each of his four years in the league with the Bills. While primarily tasked with blocking, Smith also earned 144 yards and three touchdowns on 20 receptions in 56 career games. Last season he recorded his most receptions, catching seven of the eight passes thrown to him for 42 yards and a touchdown.
Smith was picked in the fifth round of the 2011 NFL Draft by the New England Patriots.
According to ESPN's Adam Caplan, Smith will likely sign a multi-year deal with Oakland.
Oakland finished last year 3-13, and in last place in the AFC West. The team was No. 31 in points scored and No. 32 in yards gained.