The 30-year-old right-hander was obtained in a trade that sent Ty Wigginton to Houston last July. Wheeler was 0-5 with a 5.76 ERA in 25 appearances for the Rays after going 1-4 with a 5.07 ERA in 45 games with the Astros.
Wheeler's 216 appearances over the past three years are the eighth-most in the major leagues. He set career highs for innings (74 2/3) and strikeouts (82) in 2007, including 26 strikeouts in 25 innings for Tampa Bay.
Wheeler, who earned $2.1 million last season, has appeared in 71 or more games each of the last three years. In addition to his base salary in 2008, he can earn an additional $25,000 for making 65 appearances.