The offer sheet was originally reported by the St. Paul Pioneer-Press. It was then confirmed by agent David Lee.
"We signed it this morning," Lee said. "We'll just have to see what happens."
Tahi has only 23 touches in three seasons with the Minnesota Vikings, didn't register a rushing attempt in 2008, and has only six carries for his career. But the former Brigham Young standout is a strong lead blocker and helped clear the way for Minnesota tailback Adrian Peterson last year.
He would fill the same lead-blocker role with the Bengals.
Because he is a restricted free agent, and Minnesota tendered him a one-year contract at $1.01 million, the Vikings retained a right of first refusal. The terms of the offer sheet, believed to be for one year, were not yet available.
The Vikings have seven days to either match the offer by Cincinnati or pass on it. If they match it, the Vikings will assume the major terms of the offer sheet. If they opt not to match, Tahi will move to the Bengals, and the Vikings will receive no compensation, because Tahi originally entered the league as an undrafted free agent.
Coincidentally, it was the Bengals who signed him in 2006.
Tahi spent some time on the Cincinnati practice squad. He was later waived, and signed with the Vikings.
For his career, Tahi has played in 26 games with five starts. He has six carries for 15 yards and no touchdowns. He also has 17 catches for 44 yards and no touchdowns. Last season, Tahi started five of the 16 games in which he played.
Tahi is the fourth restricted free agent to sign an offer sheet with a different team this year. The other three were all matched by their incumbent teams.
Senior writer Len Pasquarelli covers the NFL for ESPN.com.