First-Class Bowling Against Each Opponent Iain O'Brien
| Opponent | Balls | Mdns | Runs | Wkts | BB | Ave | 5wI | 10wM |
| Auckland | 1831 | 97 | 756 | 45 | 8-55 | 16.80 | 4 | 1 |
| Australia | 660 | 20 | 410 | 9 | 3-111 | 45.55 | 0 | 0 |
| Bangladesh | 607 | 34 | 211 | 15 | 3-31 | 14.06 | 0 | 0 |
| Canterbury | 2262 | 97 | 1049 | 49 | 6-55 | 21.40 | 4 | 0 |
| Central Districts | 1977 | 84 | 962 | 42 | 5-42 | 22.90 | 1 | 0 |
| Derbyshire | 375 | 14 | 159 | 10 | 6-87 | 15.90 | 1 | 0 |
| England | 396 | 15 | 185 | 8 | 4-74 | 23.12 | 0 | 0 |
| England Lions | 90 | 4 | 44 | 1 | 1-44 | 44.00 | 0 | 0 |
| England XI | 204 | 5 | 132 | 6 | 4-34 | 22.00 | 0 | 0 |
| Essex | 373 | 16 | 182 | 7 | 3-46 | 26.00 | 0 | 0 |
| Glamorgan | 324 | 6 | 151 | 5 | 2-52 | 30.20 | 0 | 0 |
| Gloucestershire | 410 | 17 | 183 | 10 | 7-48 | 18.30 | 1 | 0 |
| India | 755 | 29 | 452 | 9 | 3-103 | 50.22 | 0 | 0 |
| India A | 210 | 13 | 72 | 4 | 3-30 | 18.00 | 0 | 0 |
| Kent | 252 | 11 | 137 | 0 | | | | |
| Leicestershire | 60 | 0 | 51 | 1 | 1-51 | 51.00 | 0 | 0 |
| Middlesex | 329 | 13 | 184 | 10 | 6-39 | 18.40 | 1 | 0 |
| New South Wales | 186 | 4 | 125 | 4 | 3-73 | 31.25 | 0 | 0 |
| Northern Districts | 1090 | 47 | 509 | 20 | 4-64 | 25.45 | 0 | 0 |
| Otago | 1351 | 64 | 627 | 23 | 5-39 | 27.26 | 1 | 0 |
| Pakistan | 861 | 25 | 448 | 15 | 4-35 | 29.86 | 0 | 0 |
| Pakistanis | 126 | 4 | 73 | 0 | | | | |
| South Africa | 327 | 15 | 192 | 3 | 2-78 | 64.00 | 0 | 0 |
| South Africa A | 126 | 3 | 74 | 1 | 1-74 | 74.00 | 0 | 0 |
| Sri Lanka | 398 | 7 | 320 | 6 | 2-73 | 53.33 | 0 | 0 |
| Sri Lanka A | 228 | 13 | 136 | 2 | 1-45 | 68.00 | 0 | 0 |
| Sri Lanka Cricket XI | 96 | 2 | 56 | 2 | 2-56 | 28.00 | 0 | 0 |
| Sussex | 383 | 7 | 227 | 5 | 3-65 | 45.40 | 0 | 0 |
| West Indies | 390 | 13 | 211 | 8 | 6-75 | 26.37 | 1 | 0 |
| Worcestershire | 168 | 5 | 74 | 2 | 1-27 | 37.00 | 0 | 0 |