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| Name | Pos | Team | Age | DOB | POB | Nationality | Bats | Throws | Height | Weight | Salary |
| O'Brien, Paul | MR | Santa Fe Diablos | 23 | 02/04/1995 | Davenport | USA | Right | Right | 6' 0" | 220 lbs | - |
| O'Brien, Steven | MR | Key West Barracudas | 22 | 12/25/1996 | Elmont | USA | Left | Right | 6' 3" | 245 lbs | - |
| Ohayashi, Shotaro | MR | Wichita Wranglers | 31 | 06/16/1987 | Harue | JPN | Left | Left | 6' 0" | 217 lbs | - |
| Oldreave, Tim | SP | West Palm Reds | 29 | 05/26/1989 | Hayward | USA | Right | Right | 6' 0" | 235 lbs | - |
| Olvera, Sergio | SS | West Virginia Power | 22 | 07/22/1996 | Santo Domingo | DOM | Right | Right | 6' 4" | 210 lbs | - |
| Onishi, Yoriyuki | 1B | Memphis Blues | 24 | 04/09/1994 | Tsuru | JPN | Right | Right | 6' 1" | 215 lbs | - |
| Orama, Vicente | LF | Key West Barracudas | 31 | 12/06/1987 | Totonicapan | GUA | Right | Right | 5' 8" | 202 lbs | - |
| Ortega, Sancho | MR | Montgomery Biscuits | 24 | 03/19/1994 | Jacksonville | USA | Right | Right | 6' 4" | 205 lbs | - |
| Ortíz, Armando | 1B | Montgomery Biscuits | 24 | 11/21/1994 | Santo Domingo | DOM | Left | Right | 6' 0" | 156 lbs | - |
| Osborne, Jeff | SP | West Palm Reds | 28 | 01/28/1990 | Mobile | USA | Switch | Right | 6' 2" | 220 lbs | - |
| Osborne, William | 3B | Memphis Blues | 24 | 06/09/1994 | West Lafayette | USA | Right | Right | 5' 11" | 170 lbs | - |
| Ovies, Sancho | RF | West Virginia Power | 21 | 08/12/1997 | Santiago de Cuba | CUB | Right | Right | 5' 11" | 210 lbs | - |
