| Career - Worst ERA | |||
| Rk | Player Name | Totals | |
| 1 | Clayton Richard | 5.79 | |
| 2 | John Maine | 5.58 | |
| 3 | Terry Adams | 5.04 | |
| 4 | Dan Straily | 5.00 | |
| 5 | John Thomson | 4.98 | |
| 6 | A.J. Burnett | 4.80 | |
| 7 | Steven Matz | 4.76 | |
| 8 | Brett Anderson | 4.73 | |
| 9 | Rheal Cormier | 4.71 | |
| 10 | Mark Redman | 4.70 | |
| 11 | Alex Fernandez | 4.67 | |
| 12 | Curt Schilling | 4.51 | |
| 13 | Denny Neagle | 4.40 | |
| 14 | Erik Hanson | 4.40 | |
| 15 | Johnny Cueto | 4.38 | |
| 16 | Bronson Arroyo | 4.32 | |
| 17 | Tyler Wells | 4.24 | |
| 18 | Marcus Stroman | 4.10 | |
| 19 | Joe Saunders | 4.09 | |
| 20 | Cole Hamels | 4.09 | |
| 21 | Ken Hill | 3.96 | |
| 22 | Miles Mikolas | 3.80 | |
| 23 | Brandon Webb | 3.76 | |
| 24 | Roger Clemens | 3.72 | |
| 25 | Kevin Brown | 3.70 | |
| Single Season - Worst ERA | |||||
| Rk | Player Name | Totals | Year | ||
| 1 | Mike Morgan | 7.50 | 1994 | ||
| 2 | Rheal Cormier | 6.90 | 1994 | ||
| 3 | Tom Glavine | 6.59 | 2000 | ||
| 4 | Bud Norris | 6.40 | 2014 | ||
| 5 | Shane Reynolds | 6.29 | 2002 | ||
| 6 | Clayton Richard | 6.20 | 2011 | ||
| 7 | Steve Woodard | 6.04 | 2000 | ||
| 8 | Bruce Chen | 6.03 | 2012 | ||
| 9 | Cole Hamels | 5.94 | 2017 | ||
| 10 | Adam Wainwright | 5.94 | 2020 | ||
| 11 | Eric Lauer | 5.90 | 2020 | ||
| 12 | Terry Adams | 5.80 | 2003 | ||
| 13 | Ramon Ortiz | 5.71 | 2002 | ||
| 14 | Don Robinson | 5.70 | 1990 | ||
| 15 | Kwang Hyun Kim | 5.70 | 2022 | ||
| 16 | Roger Clemens | 5.67 | 1994 | ||
| 17 | John Maine | 5.66 | 2008 | ||
| 18 | Jon Garland | 5.65 | 2003 | ||
| 19 | Ted Lilly | 5.65 | 2012 | ||
| 20 | Miles Mikolas | 5.64 | 2020 | ||
| 21 | Alex Fernandez | 5.63 | 1995 | ||
| 22 | Ervin Santana | 5.63 | 2011 | ||
| 23 | Danny Jackson | 5.62 | 1990 | ||
| 24 | Jeff Niemann | 5.60 | 2010 | ||
| 25 | Bud Norris | 5.59 | 2015 | ||