Singleton, 22, who entered this season as the club's No. 2 prospect per Baseball America, posted 17 doubles, 11 home runs, 44 RBI, 59 walks and a .351 on-base percentage in 90 minor league games in 2013. He played his last 73 games with Triple A Oklahoma City and finished strong, hitting .250 (22x88) with 19 RBI and 22 walks for a .400 on-base percentage in August.
Valdes, 35, made 17 appearances, including one start, in two stints with the Phillies this season. In his 35.0 Major League innings, Valdes allowed just a .229 (11x48) opponent's batting average vs. left-handed hitters. He posted solid numbers with Triple A Lehigh Valley in 14 starts this year, compiling a 4-5 record and a 2.86 ERA (25ER/78.2IP). Valdes has pitched in parts of four Major League seasons with New York-NL (2010), St. Louis (2011), New York-AL (2011) and Philadelphia (2012-13) and owns a 4.94 ERA (75ER/136.2IP) in 95 appearances.
Humber, 30, made 17 appearances, including seven starts, across two stints with the Astros this season. He tossed a total of 54.2 innings and pitched to a 4.74 ERA (10ER/19IP) over his final eight relief appearances. Humber was originally acquired by Houston off waivers from the White Sox and subsequently signed to a one-year deal with a club option for 2014 on Nov. 30, 2012.
Clark, 33, appeared in 16 games for the Astros this season, making 10 starts behind the plate. In his limited Major League duty, Clark caught seven of 13 attempting basestealers. He was originally signed as a minor league free agent in March of 2013.
Laird, 26, had two stints with Houston this season, appearing in 25 games. He had five homers and 11 RBI, and made 16 starts in what was his second season with the organization. Laird was originally claimed off waivers from the Yankees in September of 2012.
Pagnozzi, 25, was acquired from Atlanta in exchange for cash considerations on Sept. 3, 2013, and added to the Astros active roster. He appeared in nine games for Houston, making six starts behind the dish.
With the additions of Singleton and Valdes and the removals of Humber, Clark, Laird and Pagnozzi, the Astros 40-man roster is now at 38 players.