| Career - Worst ERA | |||
| Rk | Player Name | Totals | |
| 1 | Greg Maddux | 5.63 | |
| 2 | Javier Vazquez | 5.38 | |
| 3 | Pat Hentgen | 5.31 | |
| 4 | Mark Gardner | 5.11 | |
| 5 | Joe Magrane | 4.92 | |
| 6 | Tim Hudson | 4.72 | |
| 7 | Randy Johnson | 4.57 | |
| 8 | Mark Portugal | 4.50 | |
| 9 | Paul Maholm | 4.35 | |
| 10 | Chris Young | 4.29 | |
| 11 | David Wells | 4.28 | |
| 12 | Chien-Ming Wang | 4.28 | |
| 13 | Livan Hernandez | 4.24 | |
| 14 | Jack Morris | 4.16 | |
| 15 | Felix Hernandez | 4.16 | |
| 16 | Kevin Brown | 4.12 | |
| 17 | Orlando Hernandez | 4.12 | |
| 18 | Francisco Cordova | 4.00 | |
| 19 | John Lackey | 3.93 | |
| 20 | Brad Keller | 3.92 | |
| 21 | Alex Cobb | 3.81 | |
| 22 | Brandon McCarthy | 3.67 | |
| 23 | Matt Harvey | 3.67 | |
| 24 | Jesse Hahn | 3.62 | |
| 25 | Josh Beckett | 3.59 | |
| Single Season - Worst ERA | |||||
| Rk | Player Name | Totals | Year | ||
| 1 | Javier Vazquez | 7.20 | 2001 | ||
| 2 | Pat Hentgen | 7.17 | 1994 | ||
| 3 | Mark Portugal | 6.68 | 1994 | ||
| 4 | Mike Foltynewicz | 6.02 | 2020 | ||
| 5 | Mark Portugal | 5.87 | 1995 | ||
| 6 | Jamie Moyer | 5.79 | 1994 | ||
| 7 | Sterling Hitchcock | 5.72 | 2000 | ||
| 8 | Shawn Boskie | 5.57 | 1997 | ||
| 9 | Mark Gardner | 5.54 | 1999 | ||
| 10 | Joe Magrane | 5.53 | 1991 | ||
| 11 | Jack Morris | 5.52 | 1991 | ||
| 12 | John Cerutti | 5.44 | 1990 | ||
| 13 | Tim Wakefield | 5.43 | 2002 | ||
| 14 | Kirk Rueter | 5.37 | 1994 | ||
| 15 | Anibal Sanchez | 5.35 | 2011 | ||
| 16 | Chris Young | 5.29 | 2007 | ||
| 17 | Kenny Rogers | 5.20 | 2001 | ||
| 18 | Trevor Cahill | 5.13 | 2019 | ||
| 19 | Randy Johnson | 5.12 | 1991 | ||
| 20 | Mark Gardner | 5.04 | 1997 | ||
| 21 | Greg Maddux | 5.02 | 2008 | ||
| 22 | Armando Reynoso | 5.01 | 2000 | ||
| 23 | Jonathan Sanchez | 4.99 | 2011 | ||
| 24 | Tony Gonsolin | 4.99 | 2020 | ||
| 25 | Paul Maholm | 4.93 | 2012 | ||