Defensive end Chaz Nelson became the third junior college player to sign with Oklahoma this month when he signed just before Christmas.
Nelson (6-3, 240) had been committed to the Sooners since late November but waited until he returned home to Ohio on Friday before signing.
The Garden City (Kan.) Community College product has two years of eligibility remaining.
Juco tight end Brannon Green and defensive back Kass Everett had previously signed with the Sooners.
All are expected to enroll in January.
Everett initially announced he would sign with Texas Tech before changing his mind and signing with OU.
Nelson could get quick playing time in Norman with Frank Alexander's departure and Ronnell Lewis' expected departure opening up playing time on the defensive line.
His other offers included Baylor, Iowa State, Kansas State, Texas Tech and Illinois.
Nelson is one of two defensive ends expected to be a part of this signing class, with Baltimore high school product Charles Tapper also committed to the Sooners. Euless (Texas) Trinity defensive end Polo Manukainiu was a long-time OU commit but said his offer was pulled after he took other visits.
The Sooners are also still recruiting Mario Edwards, the top defensive end in the class of 2012.