The Houston Astros placed right-hander Roy Oswalt on the 15-day disabled list prior to their game with the Chicago Cubs on Tuesday and purchased the contract of left-handed pitcher Phillip Barzilla from Triple-A Round Rock. To make room for Barzilla on the 40-man roster, the Astros transferred right-hander Brandon Backe from the 15-day to the 60-day disabled list. Barzilla, a former Rice University pitcher, is in uniform for Tuesday's game.