Fox Sports' Ken Rosenthal is reporting that Roy Oswalt's deal with the Texas Rangers is incentive based by the sole metric of participation, likely based on concerns about the history of the right-hander's back injuries:

Source: Oswalt deal with #Rangers will be between $5M and $6M, pro-rated for amount of time he spends with team.

— Ken Rosenthal (@Ken_Rosenthal) May 29, 2012

ESPN is reporting a slightly different number, but a similar deal structure based on participation, and also how fast he can join the club:

Sources told ESPN's Karl Ravech that if Oswalt is called up by July 1, he gets $8 million pro-rated -- 4 million in his pocket. He can also earn an extra $1 million in incentives if he makes 10 starts.

Obviously, Texas' offer was reliant on Oswalt's health. The 34-year-old three-time All-Star has 115 career wins, but was a dismal 9-10 last season for Philadelphia.

For more on the Texas Rangers and Roy Oswalt, check out Baseball Nation and Lone Star Ball.