BALTIMORE -- The Orioles may not know who will replace Radhames Liz in the starting rotation, but they know they have plenty of options. Prospects Hayden Penn and Brad Bergesen are among the early favorites for a promotion to the parent club and further separated themselves from the pack by providing impressive starts on Monday night.

Penn, who has some Major League experience, is 5-6 with a 4.98 ERA for Triple-A Norfolk this year. Bergesen, meanwhile, is 13-3 with a 2.68 ERA for Double-A Bowie and has a 3-0 mark and a 1.35 ERA in his last three outings. Those performances haven't gone unnoticed, and Baltimore manager Dave Trembley said Tuesday that he's been intrigued by the pair.

"They said his curveball was better," he said of Penn. "He's got to string together some consistent starts in a row, and then he gives you an option. Bergesen had a good game and he's 13-3 at Bowie. We're aware of what those guys are doing."

Penn has been on the radar map for quite some time, as he became just the third Orioles pitcher since 1967 to make his Major League debut before the age of 21. That came in 2005, and each of the last two seasons have been interrupted by injury. Bergesen, meanwhile, is a former fourth-round pick who has just come into his own this season.

Trembley has said that he doesn't want to rush pitchers, which may lead one to believe that he'd prefer to see Bergesen make the incremental step to Triple-A before he gets called up to Baltimore. But Trembley discussed that potential development on Tuesday and said he'd have to consult with Andy MacPhail, the team's president of baseball operations.

"I think both would agree we'd rather take the conservative route," he said. "I think you have to make sure before guys come up here that they're ready physically and mentally, not only to compete, but to have a certain amount of success. If that means taking the time and taking it one level at a time, that's the way we're going to do it. But I don't think I'm opposed or Andy's opposed to moving somebody up here from Double-A if they're ready to go. I think you have to almost be pretty sure."