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| League History Index | Players | Teams | Managers | Leagues | Leaderboards | Awards | Accomplishments |
| Player | From-To | W | L | Pct | ERA | G | GS | CG | SHO | SV | IP | H | ER | HR | BB | SO |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dan O'Brien | 1978-1981 | 8 | 7 | .533 | 3.01 | 97 | 2 | 0 | 0 | 1 | 152.2 | 127 | 51 | 12 | 82 | 85 |
| Randy O'Neal | 1985-1993 | 34 | 29 | .540 | 3.41 | 149 | 78 | 3 | 1 | 23 | 596.1 | 535 | 226 | 64 | 192 | 349 |
| Blue Moon Odom | 1976-1979 | 10 | 14 | .417 | 4.29 | 139 | 7 | 0 | 0 | 3 | 323.0 | 319 | 154 | 24 | 177 | 179 |
| Chad Ogea | 1994-1996 | 15 | 16 | .484 | 5.43 | 65 | 48 | 0 | 0 | 1 | 331.2 | 333 | 200 | 70 | 102 | 282 |
| Bob Ojeda | 1982-1998 | 185 | 137 | .575 | 3.72 | 417 | 417 | 66 | 16 | 0 | 2898.2 | 2638 | 1197 | 331 | 879 | 2026 |
| Steve Olin | 1989-1996 | 8 | 6 | .571 | 3.41 | 85 | 0 | 0 | 0 | 3 | 171.1 | 133 | 65 | 29 | 41 | 110 |
| Omar Olivares | 1991-1997 | 23 | 13 | .639 | 3.67 | 50 | 40 | 11 | 0 | 0 | 316.1 | 266 | 129 | 37 | 133 | 198 |
| Darren Oliver | 1993-1998 | 30 | 55 | .353 | 6.01 | 126 | 123 | 2 | 0 | 0 | 629.0 | 645 | 420 | 136 | 299 | 517 |
| Francisco Oliveras | 1989-1998 | 21 | 33 | .389 | 5.59 | 200 | 29 | 0 | 0 | 15 | 431.1 | 484 | 268 | 94 | 157 | 339 |
| Al Olmsted | 1980-1983 | 0 | 3 | .000 | 5.18 | 35 | 0 | 0 | 0 | 0 | 57.1 | 64 | 33 | 5 | 28 | 37 |
| Gregg Olson | 1988-1998 | 33 | 17 | .660 | 2.87 | 347 | 0 | 0 | 0 | 39 | 496.0 | 354 | 158 | 31 | 272 | 487 |
| Steve Ontiveros | 1985-1995 | 39 | 28 | .582 | 4.35 | 439 | 12 | 1 | 1 | 14 | 717.2 | 723 | 347 | 97 | 329 | 445 |
| Mike Oquist | 1993-1996 | 1 | 3 | .250 | 6.58 | 19 | 9 | 0 | 0 | 0 | 64.1 | 72 | 47 | 17 | 28 | 59 |
| Jesse Orosco | 1979-1992 | 36 | 48 | .429 | 3.73 | 470 | 0 | 0 | 0 | 90 | 564.1 | 433 | 234 | 64 | 390 | 589 |
| Donovan Osborne | 1992-1996 | 24 | 38 | .387 | 4.81 | 112 | 72 | 3 | 1 | 4 | 530.0 | 542 | 283 | 92 | 151 | 440 |
| Al Osuna | 1990-1990 | 0 | 2 | .000 | 10.29 | 6 | 0 | 0 | 0 | 0 | 7.0 | 9 | 8 | 0 | 6 | 4 |
| Antonio Osuna | 1995-1998 | 17 | 10 | .630 | 3.99 | 131 | 0 | 0 | 0 | 41 | 169.0 | 144 | 75 | 27 | 95 | 169 |
| Jim Otten | 1976-1980 | 12 | 8 | .600 | 2.81 | 118 | 0 | 0 | 0 | 17 | 186.0 | 177 | 58 | 7 | 89 | 97 |
| Dave Otto | 1987-1988 | 5 | 5 | .500 | 5.86 | 28 | 12 | 0 | 0 | 1 | 101.1 | 122 | 66 | 13 | 42 | 42 |
| Mike Overy | 1977-1981 | 3 | 9 | .250 | 3.41 | 186 | 0 | 0 | 0 | 47 | 208.2 | 188 | 79 | 22 | 89 | 154 |
| Bob Owchinko | 1976-1979 | 10 | 10 | .500 | 4.09 | 66 | 17 | 0 | 0 | 0 | 154.0 | 164 | 70 | 6 | 74 | 76 |
