O'Sullivan made 89 appearances for Swindon after coming up through the youth ranks, most of them in the Second Division championship season of 1995/1996, where his performances earned him a call-up to the Irish under-21 squad. He was not used regularly in Division One the following season, and because of the lack of first-team opportunities, he requested a transfer - resulting in his move to Cardiff.
| Season | LEAGUE | POST-SEASON | FA CUP | EFL CUP | EUROPE | OTHER | TOTAL | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Apps | Gls | Apps | Gls | Apps | Gls | Apps | Gls | Apps | Gls | Apps | Gls | Apps | Gls | |
| 1996/97 | 16 (+9) | - | - | - | 0 (+1) | - | 2 | 1 | - | - | - | - | 18 (+10) | 1 |
| 1995/96 | 27 (+7) | 3 | - | - | 1 | - | 4 | - | - | - | 0 (+2) | - | 32 (+9) | 3 |
| 1994/95 | 22 (+8) | - | - | - | 0 (+2) | - | 5 | - | 2 | - | - | - | 29 (+10) | - |
| 1993/94 | - | - | - | - | - | - | - | - | - | - | - | - | - | - |
| 1992/93 | - | - | - | - | - | - | - | - | 1 | - | - | - | 1 | - |
| 1991/92 | - | - | - | - | - | - | - | - | - | - | - | - | - | - |
| 1990/91 | - | - | - | - | - | - | - | - | - | - | - | - | - | - |
| 1989/90 | - | - | - | - | - | - | - | - | - | - | - | - | - | - |
| TOTAL | 65 (+24) | 3 | - | - | 1 (+3) | - | 11 | 1 | 3 | - | 0 (+2) | - | 80 (+29) | 4 |
Note that appearance data for reserve and youth teams may not be complete. Expand for more information.
| Season | LEAGUE | POST-SEASON | YTH CUP | YTH LC | TOTAL | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| Apps | Gls | Apps | Gls | Apps | Gls | Apps | Gls | Apps | Gls | |
| 1996/97 | - | - | - | - | - | - | - | - | - | - |
| 1995/96 | - | - | - | - | - | - | - | - | - | - |
| 1994/95 | - | - | - | - | - | - | - | - | - | - |
| 1993/94 | - | - | - | - | - | - | - | - | - | - |
| 1992/93 | - | - | - | - | - | - | - | - | - | - |
| 1991/92 | 1 | 1 | - | - | - | - | - | - | 1 | 1 |
| 1990/91 | 9 | 2 | - | - | - | - | - | - | 9 | 2 |
| 1989/90 | 15 | 1 | - | - | - | - | - | - | 15 | 1 |
| TOTAL | 25 | 4 | - | - | - | - | - | - | 25 | 4 |