"He had a better fastball, and his stuff was better, also," said Rockies pitching coach Jim Wright, who had not spoken to Oswalt, but received a report on the outing.
Oswalt, a three-time All-Star, signed with the Rockies on May 3.
Thomas Harding is a reporter for MLB.com. Read his blog, Hardball in the Rockies, and follow him on Twitter @harding_at_mlb. This story was not subject to the approval of Major League Baseball or its clubs.