 | | | | Av Time | | | Place | Races | 1st | 2nd | 3rd | Trophies | |
|---|
 O'brien Simon | 28.9 | | | 101 | 1 | 0 | 0 | 0 | | |
| 2015 | FB | 28:56:58 | | Greensmith Ben & O'brien Simon | Independent | 101 | | | | | Tyne | |
| O'Byme Sheila | 21.8 | | | 6 | 1 | 0 | 0 | 0 | | |
| 1983 | | 21:47:57 | | Garrett Mary & O'Byme Sheila | Richmond & Argonauts - Cork | 6 | | | | | Ladies | |
| O'Byrne Sheila | 20.8 | | | 13 | 1 | 0 | 0 | 0 | | |
| 1984 | | 20:46:05 | | Garrett Mary & O'Byrne Sheila | Richmond & Argonauts - Cork | 13 | | | | | Ladies | |
| O'Callaghan Kevin | 22.8 | | | 22 | 1 | 0 | 0 | 0 | | |
| 2012 | | 22:45:47 | | O'Callaghan Kevin & Young Shane | Independent | 22 | | | | | | |
| O'Cearbhaill Derek | 26.6 | | | 25 | 1 | 0 | 0 | 0 | | |
| 2003 | C2 | 26:33:45 | | O'Cearbhaill Derek & Knight David | Dingle | 25 | | | | | | |
| O'Connell Andrew | 24.0 | | | 12 | 1 | 0 | 0 | 0 | | |
| 2003 | | 23:57:59 | | O'Connell Andrew & Tyrrell Paul | Malahide Sea Scouts | 12 | | | | | Scouts | |
| O'connell Elly | 23.6 | | | 42 | 1 | 0 | 0 | 0 | | |
| 2019 | | 23:37:57 | | O'connell Elly & Channon Peter | Richmond | 42 | | | | | | |
| O'Connor E C | 49.1 | | | 60 | 1 | 0 | 0 | 0 | | |
| 1967 | | 49:08:00 | | Hopkins T C & O'Connor E C | Tweeddale Boys club | 60 | | | | | | |
| O'Connor W H | 25.7 | | | 24 | 1 | 0 | 0 | 0 | | |
| 1967 | | 25:44:00 | | Jones K E & O'Connor W H | Borough Road College | 24 | | | | | | |
| O'Donovan D | 18.5 | | | 3 | 3 | 1 | 1 | 0 | | |
| 1982 | | 17:09:12 | | O'Donovan J & O'Donovan D | | 5 | | | | | | |
| 1983 | | 19:56:50 | | O'Donovan D & Kennedy J J | Argonauts - Cork | 1 | | 1 | | | Civilian | |
| 1985 | | 18:27:10 | | O'Donovan D & Kennedy J J | Richmond | 2 | | | 1 | | | |
| O'Donovan J | 17.1 | | | 5 | 1 | 0 | 0 | 0 | | |
| 1982 | | 17:09:12 | | O'Donovan J & O'Donovan D | | 5 | | | | | | |
| O'Geran Conor | 26.2 | | | 52 | 1 | 0 | 0 | 0 | | |
| 2002 | | 26:10:07 | | O'Geran Conor & Brett Victor | Phoenix | 52 | | | | | | |
| O'grady Geoff | 27.9 | | | 95 | 1 | 0 | 0 | 0 | | |
| 2017 | | 27:51:47 | | Durrant John & O'grady Geoff | Wey Kc | 95 | | | | | | |
| O'Grady Jon | 17.1 | | | 2 | 2 | 1 | 0 | 1 | | |
| 2025 | | 17:25:09 | | Butler Billy & O'Grady Jon | International & Runcorn | 3 | | | | 1 | Lee | |
| 2026 | | 16:46:17 | | Butler Billy & O’Grady Jon | Falcon & Runcorn | 1 | | 1 | | | Civilian,Lee | |
| O'grady Jon (Teddington) | 14.2 | | | 2 | 1 | 0 | 1 | 0 | | |
| 2024 | | 14:09:05 | | Butler Billy & O'grady Jon | Falcon & Runcorn | 2 | | | 1 | | | |
| O'hagan Stuart | 30.7 | | | 100 | 1 | 0 | 0 | 0 | | |
| 2011 | | 30:43:06 | | Hoskin Shaun & O'hagan Stuart | Royal Logistic Corps | 100 | | | | | | |
| O'Keefe P C | 29.6 | | | 18 | 1 | 0 | 0 | 0 | | |
| 1968 | | 29:36:30 | | O'Keefe P C & Noonan P | 35 Corps Engineer Regt | 18 | | | | | | |
| O'Keefe R | 20.6 | | | 1 | 1 | 1 | 0 | 0 | | |
| 1961 | | 20:37:05 | | Crook W & O'Keefe R | 1st Lancs & 1st Mddx & Richmond | 1 | | 1 | | | | |
| O'keeffe Isabel | 25.7 | | | 67 | 1 | 0 | 0 | 0 | | |
| 2016 | | 25:41:40 | | O'keeffe Isabel & O'keeffe Rosanna | Devizes | 67 | | | | | | |
| O'keeffe Rosanna | 25.7 | | | 67 | 1 | 0 | 0 | 0 | | |
| 2016 | | 25:41:40 | | O'keeffe Isabel & O'keeffe Rosanna | Devizes | 67 | | | | | | |
| O'Kelly F P | 60.0 | | | 107 | 1 | 0 | 0 | 0 | | |
| 1995 | | 60:02:37 | | Smerdon A P & O'Kelly F P | Independent | 107 | | | | | | |
| O'leary David | 24.5 | | | 27 | 1 | 0 | 0 | 0 | | |
| 2026 | | 24:31:15 | | O'leary David & Ryan Timmy | International | 27 | | | | | | |
| O'Mahony P A | 33.7 | | | 84 | 4 | 0 | 0 | 0 | | |
| 1983 | | 51:29:06 | | Hollands S J & O'Mahony P A | Phoenix Venture Scouts | 77 | | | | | | |
| 1984 | | 33:41:15 | | O'Mahony P A & Hollands S J | Phoenix Venture Scouts | 120 | | | | | | |
| 1992 | | 27:11:35 | | Flynn M & O'Mahony P A | Royal Navy | 87 | | | | | | |
| 1993 | | 22:28:25 | | Fiynn M C & O'Mahony P A | RNKA & Venture Scouts | 53 | | | | | | |
| O'Malley T | 25.6 | | | 80 | 2 | 0 | 0 | 0 | | |
| 1984 | | 26:18:20 | | Stack P G & O'Malley T | Leaside | 87 | | | | | | |
| 1985 | | 24:52:07 | | Stack P G & O'Malley T | Leaside & NCYC | 72 | | | | | | |
| O'Meara Michael | 18.0 | | | 2 | 4 | 3 | 0 | 1 | | |
| 1996 | | 18:50:35 | | Fanning B & O'Meara Michael | Independent | 3 | | | | 1 | | |
| 1999 | | 17:51:30 | | Morrissey Jim & O'Meara Michael | Dollymount Sea Scouts & 180 Waterford | 1 | | 1 | | | Civilian | |
| 2002 | | 16:54:16 | | Morrissey Jim & O'Meara Michael | Dollymount Sea Scouts & 180 Waterford | 1 | | 1 | | | Civilian | |
| 2003 | | 18:35:41 | | Morrissey Jim & O'Meara Michael | Dollymount Sea Scouts & 180 Waterford | 1 | | 1 | | | Civilian | |
| O'Neil M T | 35.6 | | | 126 | 1 | 0 | 0 | 0 | | |
| 1988 | | 35:35:30 | | Longworth S J & O'Neil M T | RMA Sandhurst | 126 | | | | | | |
| O'Neill B | 21.0 | | | 32 | 1 | 0 | 0 | 0 | | |
| 1982 | | 21:02:22 | | O'Neill B & Macdonald A M | Liverpool University | 32 | | | | | | |
| O'neill Joseph | 23.9 | | | 41 | 1 | 0 | 0 | 0 | | |
| 2017 | | 23:53:56 | | O'neill Joseph & Rynn Sean | RMKA | 41 | | | | | | |
| O'Smotherly P J | 21.5 | | | 11 | 1 | 0 | 0 | 0 | | |
| 1998 | | 21:28:10 | | O'Smotherly P J & Crowson D N | Royal Engineers | 11 | | | | | | |
| O'Sullivan A V | 22.7 | | | 31 | 1 | 0 | 0 | 0 | | |
| 1980 | | 22:42:16 | | Helps E J & O'Sullivan A V | Newham | 31 | | | | | | |
| O'Sullivan B B | 23.9 | | | 17 | 1 | 0 | 0 | 0 | | |
| 1967 | | 23:56:00 | | Smart G W & O'Sullivan B B | 9th Ind Para Sqn RE | 17 | | | | | | |
| O Hanrahan Feargal | 25.1 | | | 69 | 1 | 0 | 0 | 0 | | |
| 2015 | | 25:03:31 | | Irwin William & O Hanrahan Feargal | Wwkc Ireland | 69 | | | | | | |
| O Keeffe Eavan | 16.8 | | | 2 | 1 | 0 | 1 | 0 | | |
| 2023 | | 16:45:55 | | Horkan David & O Keeffe Eavan | International & Celbridge Paddlers | 2 | | | 1 | | European | |
| Oakley Robin | 22.4 | | | 40 | 1 | 0 | 0 | 0 | | |
| 2009 | C2 | 22:26:27 | | Oakley Robin & Collison Chris | Hemel Hempstead | 40 | | | | | | |
| Oaten J E | 37.9 | | | 152 | 1 | 0 | 0 | 0 | | |
| 1987 | | 37:52:19 | | Edwards S N & Oaten J E | Viking | 152 | | | | | | |
| Oates A J | 43.6 | | | 97 | 2 | 0 | 0 | 0 | | |
| 1983 | | 50:40:06 | | Oates A J & James D | 10th Wakefield Scouts | 73 | | | | | | |
| 1986 | | 36:33:10 | | Delany D M & Oates A J | Pangbourne Advent. Dolphin | 120 | | | | | | |
| Oconnell Elly | 19.8 | | | 19 | 1 | 0 | 0 | 0 | | |
| 2023 | | 19:46:39 | | Oconnell Elly & Herwanger Jorg | Richmond | 19 | | | | | | |
| Offer T D | 23.4 | | | 62 | 1 | 0 | 0 | 0 | | |
| 1993 | | 23:21:58 | | Gerrard M F & Offer T D | Thames Valley Police | 62 | | | | | | |
| Offiler D | 29.4 | | | 15 | 1 | 0 | 0 | 0 | | |
| 1964 | | 29:21:25 | | Offiler D & Niven F | RAF Oakington | 15 | | | | | | |
| Ogbum W D | 31.1 | | | 73 | 2 | 0 | 0 | 0 | | |
| 1981 | | 34:45:56 | | Ogbum W D & Edyvean N J | Independent | 65 | | | | | | |
| 1982 | | 27:25:59 | | Ogbum W D & Pocock DA | Independent | 80 | | | | | | |
| Ogeman Elin | 26.4 | | | 87 | 1 | 0 | 0 | 0 | | |
| 2014 | | 26:22:55 | | Lynch Maria & Ogeman Elin | Southampton | 87 | | | | | | |
| Okopski P | 36.3 | | | 123 | 1 | 0 | 0 | 0 | | |
| 1989 | | 36:20:05 | | Gilholm A J & Okopski P | HMS Osprey | 123 | | | | | | |
| Oldham Peter | 26.4 | | | 39 | 3 | 0 | 0 | 0 | | |
| 2002 | C2 | 30:05:24 | | Broad James & Oldham Peter | Independent | 71 | | | | | | |
| 2003 | C2 | 25:58:12 | | Broad James & Oldham Peter | Independent | 21 | | | | | Canadian | |
| 2004 | C2 | 23:16:07 | | Oldham Peter & Broad James | Independent | 25 | | | | | Canadian | |