A posting on the Seahawks' Web site confirmed the deal. ESPN.com said the contract will cover six years and is valued at $48.5, more than half of which is guaranteed.
Okung, who played at Oklahoma State and was the Big 12 Lineman of the Year last season, is expected to replace Walter Jones for the Seahawks. Jones missed all of last season because of injury.
The 22-year-old Okung is 6-foot-5 and 310 pounds. He finished his career at Oklahoma State with 47 consecutive starts.