Sheets, who spent his past two seasons in the Canadian Football League, was the MVP of the Grey Cup in November when his Saskatchewan RoughRiders won the CFL's Super Bowl. In the 101st Grey Cup, Sheets ran for a game-record 197 yards as the Roughriders beat the Hamilton Tiger-Cats 45-23.
Before heading up to Canada in 2012, Sheets spent several seasons trying to latch on to an NFL roster. The 28-year-old spent time on the practice squads of both the Carolina Panthers and San Francisco 49ers. Sheets did see some NFL action in 2009 when he played in two regular season games for the Dolphins.
In two CFL seasons, Sheets totaled 2,875 yards rushing and 23 touchdowns.
Sheets probably won't be the last running back the Raiders sign this offseason. Oakland's two leading rushers rom 2013 -- Darren McFadden and Rashad Jennings -- are both free agents. The Raiders are expected to let McFadden leave in free agency, but it's likely they'll make a move to re-sign Jennings.