| Career - Worst ERA | |||
| Rk | Player Name | Totals | |
| 1 | Randy Wolf | 5.85 | |
| 2 | Tom Browning | 5.68 | |
| 3 | Tyler Alexander | 5.23 | |
| 4 | Kevin Tapani | 5.11 | |
| 5 | Jose Mesa | 5.03 | |
| 6 | A.J. Burnett | 5.03 | |
| 7 | Logan Gilbert | 4.99 | |
| 8 | Blake Snell | 4.97 | |
| 9 | Paul Abbott | 4.83 | |
| 10 | Roger Clemens | 4.82 | |
| 11 | Tim Lincecum | 4.71 | |
| 12 | Lance Lynn | 4.71 | |
| 13 | Roy Oswalt | 4.66 | |
| 14 | Jose Quintana | 4.60 | |
| 15 | Josh Collmenter | 4.35 | |
| 16 | Dave Stieb | 4.30 | |
| 17 | Zach Plesac | 4.26 | |
| 18 | Joaquin Benoit | 4.19 | |
| 19 | Tim Wakefield | 3.99 | |
| 20 | Zane Smith | 3.90 | |
| 21 | Daniel Hudson | 3.89 | |
| 22 | Miguel Gonzalez | 3.82 | |
| 23 | Kevin Appier | 3.81 | |
| 24 | Kevin Brown | 3.75 | |
| 25 | Jose Fernandez | 3.22 | |
| Single Season - Worst ERA | |||||
| Rk | Player Name | Totals | Year | ||
| 1 | Dave Stewart | 9.46 | 1994 | ||
| 2 | Jose Mesa | 8.30 | 1994 | ||
| 3 | Victor Zambrano | 7.78 | 2004 | ||
| 4 | Randy Wolf | 7.49 | 2001 | ||
| 5 | Jered Weaver | 6.95 | 2016 | ||
| 6 | Adbert Alzolay | 6.93 | 2022 | ||
| 7 | Paul Abbott | 6.79 | 2001 | ||
| 8 | R.A. Dickey | 6.70 | 2018 | ||
| 9 | Rob Bell | 6.64 | 2005 | ||
| 10 | Chase Anderson | 6.38 | 2015 | ||
| 11 | Randy Wolf | 6.13 | 2004 | ||
| 12 | Tom Browning | 6.12 | 1990 | ||
| 13 | Randy Wolf | 6.09 | 2005 | ||
| 14 | Mike Moore | 6.06 | 1994 | ||
| 15 | Tom Gorzelanny | 6.04 | 2008 | ||
| 16 | A.J. Burnett | 5.95 | 2011 | ||
| 17 | Alex Cobb | 5.88 | 2019 | ||
| 18 | Roy Oswalt | 5.82 | 2012 | ||
| 19 | Tom Gorzelanny | 5.81 | 2007 | ||
| 20 | Jose Quintana | 5.80 | 2017 | ||
| 21 | Roy Oswalt | 5.79 | 2005 | ||
| 22 | Hideo Nomo | 5.73 | 1998 | ||
| 23 | Jeremy Hellickson | 5.72 | 2018 | ||
| 24 | Aaron Sele | 5.71 | 2002 | ||
| 25 | Blake Snell | 5.68 | 2018 | ||