Jefferson, 5-foot-11, 210 pounds, is rated as the fifth-best safety and 82nd player overall by ESPN's Scouts Inc.
Stills, 6-foot, 190 pounds, is rated as the 14th-best receiver and 73rd overall player.
"We appreciate the contributions that Tony and Kenny have made during their time at Oklahoma," Oklahoma coach Bob Stoops said in a statement. "We wish them both the best as they pursue their opportunities in the NFL."
Jefferson was a second-team All-American this season after leading Oklahoma with 119 tackles. He also had two interceptions.
Stills was the team's leading receiver with 82 catches for 959 yards and 11 touchdowns.
Oklahoma's season ended Friday night with a 41-13 loss to Texas A&M in the AT&T Cotton Bowl.
Information from The Associated Press was used in this report.