The Astros are expected to select Appel, a source told ESPN senior baseball analyst Jim Bowden, the former general manager of the Nationals and the Reds. The Astros intend to keep their choice under wraps until they make the first selection at 6 p.m. CT tonight.
The Draft can be seen live on MLB Network and MLB.com.
Appel emerged as the likely top pick in recent weeks. The Astros are picking No. 1 overall for the third time in their history. They took third baseman Phil Nevin in 1992 and pitcher Floyd Banister in 1976.
Appel has made 15 starts for Stanford and has gone 10-1 with a 2.27 ERA with 127 strikeouts in 119 innings. Stanford will play in the NCAA Super Regionals this weekend in Tallahassee, Fla., against Florida State in a best-of-three series to decide which team advances to the College World Series.
Appel grew up in Houston cheering for the Astros before the family moved to California when he was 12. Houston is prepared to pay the No. 1 pick a prescribed signing bonus of $7.2 million and will have until July 13 to get the deal done.