This probably won't be the last time we write about Roy Oswalt in the Astros' History series. This 23d round draft pick made a huge impression on the Astros' franchise records. He is recent enough that there is no need to give you biographical information.
What this article focuses on is his 133 ERA+ over 10 seasons as an Astros pitcher. (As you may have guessed, today is game 133, thus the numerical association.) I will make the argument that Roy Oswalt is best pitcher in Astros' history.
The best Astros' pitcher is a subjective judgement. Some people may focus on best seasons or best single games or peaks instead of careers. My criteria is run prevention (ERA+) over a long career with the Astros. (As you probably know, ERA+ is ERA adjusted for ballparks and the run scoring era.) I also set aside the relief pitchers, like Billy Wagner, because it is hard to compare starting pitchers and closers. However, in most cases, a very good starting pitcher is more valuable than a very good relief pitcher.
Here is how Oswalt's Astros career ERA+ compares to other great Astros' pitchers.
Oswalt (10 yrs) 133
Hampton (7 yrs) 114
Ryan (9 yrs) 110
Wilson (9 yrs) 109
Forsch (11 yrs) 108
Richard (10 yrs) 108
Scott (9 yrs) 107
Reynolds (11 yrs) 106
Niekro (11 yrs) 105
Dierker (14 yrs) 103
On top of that Oswalt was the best National League starting pitcher during the period of his Astros' career. Oswalt's Astros' career spanned the 2001 to 2010 seasons. For that period, Roy Oswalt accumulated more WAR (47.4) than any other NL starting pitcher. Only Roy Halliday and C.C. Sabbathia had more WAR in the major leagues for that period.