| Name/Location | County | Open | Close | Comment |
| O'Gaunt | . | . | . | See John o'Gaunt |
| O'HANLON'S, Clyst St Lawrence | Devon | 1996 | . | Moved from Vauxhall, London 2000. Scanlon's Fine Ales also used the plant? |
| Oak Brewing Co | . | . | . | See Phoenix |
| OAKHAM ALES, Peterborough | Cambridgeshire | 1993 | . | Located at The Brewery Tap PH. Moved from Rutland 1998. Second site acquired 2006 |
| OAKHILL, Oakhill, Bath | Somerset | 1984 | 2004 | Site ex Oakhill (1767-1938) & Beacon (1981-1983) |
| OAKLEAF, Gosport | Hampshire | 2000 | . | Plant ex Planets |
| Oast House Brewery | . | . | . | See Willoughby |
| Oakwell Brewery | . | . | . | See Barnsley |
| OAKWELL, Barnsley | S Yorkshire | 1998 | . | Ex Barnsley Brewery (closed by John Smiths 1970)site |
| OBAN ALES, Kilmelford, Oban | Argyllshire | 2010 | . | Plant ex Black Mountain. Located at The Cuilfail Hotel |
| OBAN BAY, Oban | Argyllshire | 2009 | . | Plant ex Isle of Mull. Located at The Cuan Mor Hotel |
| ODCOMBE, Lower Odcombe, Yeovil | Somerset | 2005 | . | Site/plant formerly Odcombe Ales |
| ODCOMBE ALES, Lower Odcombe, Yeovil | Somerset | 2000 | 2005 | Located at The Masons Arms PH. See also Odcombe |
| OFFA'S DYKE, Trefonen | Shropshire | 2006 | . | Located at The Barley Mow PH. Plant ex Fisherrow. Closed end 2006 restarted 2007 with ex Thomas McGuiness plant |
| OKELL, Kewaigue, Douglas | I O M | 1850 | . | Acquired by Heron & Brearley 1972. Re-named IOM Breweries 1986-96. Moved from The Falcon Steam Brewery, Douglas 1994. See also Castletown |
| Old Anchor | . | . | . | See Jolly Roger, Upton on Severn |
| OLD BANK STREET, Manchester | Gtr Manchester | 1983 | 1985 | . |
| OLD BARN, Tow Law | Co Durham | 1997 | 1998 | Aka Edmundbyers |
| OLD BEAR, Keithley | W Yorkshire | 1992 | . | Moved from The Old White Bear PH, Cross Hills, Keithley 2005 |
| OLD BOG, Headington, Oxford | Oxfordshire | 2005 | . | Located at The Masons Arms PH. Plant ex Bitter End. Aka Meesons? |
| Old Brewery, Greenwich | . | . | . | See The Old Brewery |
| Old Brewery Inn | . | . | . | See Parish |
| Old Bulls Head Inn | . | . | . | See Black Country Ales |
| OLD CANNON, Bury St Edmunds | Suffolk | 1999 | . | Located at The St Edmunds Head PH |
| Old Castle | . | . | . | See Tomlinson's |
| OLD CHAPEL, Forton, Gosport | Hampshire | 1999 | 2000 | Located at The Clarence Tavern. Plant ex Hedgehog & Hogshead Southampton |
| OLD CHIDHAM, Chidham | W Sussex | 1979 | 1983 | Located at The Old House at Home PH |
| OLD CHIMNEYS, Market Weston, Diss | Suffolk | 1995 | . | . |
| Old Comical | . | . | . | See Sandown |
| OLD COTTAGE, Burton-upon- Trent | Staffordshire | 2000 | . | Plant ex Old Cottage, New Hutton. Moved from Heritage site 2001 |
| OLD COTTAGE, New Hutton | Cumbria | 1996 | 1999 | . |
| OLD COURT, Huddersfield | W Yorkshire | 1994 | 2000? | Whitbread pub brewery |
| OLD CROSS TAVERN, Hertford | Hertfordshire | 2008 | . | Located at the Old Cross Tavern |
| OLD DAIRY, Rolvenden, Cranbrook | Kent | 2010 | . | . |
| Old Fart | . | . | . | See Merrimans |
| OLD FOREIGNER, Glenkindie, Alford | Aberdeenshire | 2007 | . | Located at The Glenkindie Arms Hotel |
| Old Forge | . | . | . | See Sussex |
| Old Hall Brewery | . | . | . | See Loweswater |
| Old Hatchet | . | . | . | See Woodsman |
| Old House at Home | . | . | . | See Old Chidham |
| Old Ivy House | . | . | . | See Pheasant & Firkin |
| OLD KENT, Borough Green, Sevenoaks | Kent | 2000 | 2003 | Same ownership as Grand Union |
| OLD LAXEY, Laxey | I O M | 1997 | . | Located at The Shore Hotel |
| Old Lion | . | . | . | See Southsea |
| OLD LONDON BRIDGE, Southwark | London SE1 | 2000 | 2001? | Site (& plant?) ex Bishops |
| OLD LUXTERS, Hambleden, Henley on Thames | Buckinghamshire | 1990 | . | Operated by Chiltern Valley Wines |
| Old Market Tavern | . | . | . | See Altringham |
| OLD MILL, Snaith, Goole | E Yorkshire | 1983 | . | . |
| OLD OAK, Etchingham | E Sussex | 1982 | 1984 | Located at The DeEtchingham Arms PH. Moved from Uckfield 1983 |
| OLD PINT POT, Salford | Gtr Manchester | 1996 | 2001 | Owned by Honeycombe Leisure. Plant was also used by Bridgewater Ales |
| Old Royal George | . | . | . | See Dunn Plowman |
| OLD SPOT, Cullingworth, Bradford | W Yorkshire | 2005 | . | Plant mainly ex Boat |
| Old Stables | . | . | . | See Frankton Bagby |
| OLD STABLES, Sandy | Bedfordshire | 2002 | 2006 | Located at The Sir William Peel PH. Plant sold to Buckle Street |
| OLD SWAN, Cheltenham | Gloucestershire | 1983 | 1987 | Whitbread pub brewery |
| OLD WHEELTON, Wheelton, Chorley | Lancashire | 2001 | 2003 | Located at The Dressers Arms PH. Contract brewed by Pictish |
| Old White Bear | . | . | . | See Old Bear & Naylors |
| OLDE BULL & BUSH, Stoke-on-Trent | Staffordshire | 1986 | 1989 | Former Sea Lion. Aka Potters |
| OLDE SWAN, Netherton | W Midlands | 2001 | . | Aka 'Ma Pardoes' & also brewed 1840-1988 (one of only 4 brew pubs in 1971). Now owned by Punch Taverns |
| OLDERSHAW, Grantham | Lincolnshire | 1997 | . | Plant ex Shires, enlarged 2007 |
| OLDHAM, Oldham | Gtr Manchester | 1868 | 1989 | Albion Brewery. Acquired by Boddingtons 1982 |
| OLE SLEW FOOT, Hainford, Norwich | Norfolk | 2009 | . | . |
| OPA HEY'S, Aldeby, Beccles | Norfolk | 2008 | . | . |
| ORANGE, Pimlico | London, SW1 | 1983 | 2001 | Part of Clifton Inns (Watneys). Aka Pimlico & Bloomsbury Brewing Co. Acquired by S&N 1993 |
| ORCHARD BREWERY BAR, Barnsley | S Yorkshire | 1999 | 2003 | Part of Delta Cloud Group |
| ORCHARD, Scoreby Brook, Brigg | Lincolnshire | 1997 | 2001? | Located at The Queens Arms PH. Name changed from Brigg 1999 |
| Organic | . | . | . | See Chough |
| ORIGINAL, Basildon | Essex | 1997 | 2001 | Located at The Festival Leisure Park bowling alley (Bass) |
| ORIGINAL, Birmingham | W Midlands | 1998 | 2001 | Located at The Great Park bowling alley (Bass) |
| ORIGINAL, Bracknell | Berkshire | 1998 | 2001 | Located at The Point bowling alley (Bass) |
| ORIGINAL, Cardiff | Glamorgan | 1997 | 2001 | Located at the Cardiff bowling alley (Bass) |
| ORIGINAL, Coatbridge | Lanarkshire | 1998 | 2001 | Located at The Showcase Leisure Park bowling alley (Bass) |
| ORIGINAL, Horwich, Bolton | Lancashire | 1998 | 2001 | Located at The Middlebrok Sports Village bowling alley (Bass) |
| ORIGINAL, Leeds | W Yorkshire | 1998 | 2001 | Located at the Leeds bowling alley (Bass) |
| ORIGINAL, Leicester | Leicestershire | 1995 | 2001 | Located at The Meridian Leisure Park bowling alley - the original! (Bass) |
| ORIGINAL, North Finchley | London N12 | 1996 | 2001 | Located at The Finchley Leisure Park bowling alley (Bass) |
| ORIGINAL, Sheffield | S Yorkshire | 1998 | 2001 | Located at The Valley Entertainment bowling alley (Bass) |
| ORIGINAL, Stevenage | Hertfordshire | 1996 | 2001 | Located at The Stevenage Leisure Park bowling alley (Bass) |
| ORIGINAL, Surrey Quays | London SE16 | 1998 | 2001 | Located at Surrey Quays bowling alley (Bass) |
| ORIGINAL, Watford | Hertfordshire | 1996 | 2001 | Located at The Woodside Leisure Park bowling alley (Bass) |
| ORKNEY, Quoyloo | Orkney | 1988 | . | Formed Highlads & Islands Breweries with Orkney 2004. Acquired by Sinclair Breweries 2006 |
| OSSETT, Ossett, Wakefield | W Yorkshire | 1998 | . | Moved from The Brewers Pride PH 2005. See also Fernandes, Rat & Ratchet and Riverhead |
| OTLEY, Pontypridd | Glamorgan | 2005 | . | . |
| OTTER, Luppitt, Honiton | Devon | 1990 | . | . |
| OULTON ALES, Oulton Broad | Suffolk | 2001 | 2008 | Lake Lothing Brewery. Name changed from Green Jack 2001 |
| OULTON BROAD, Oulton Broad | Suffolk | 1987 | 1987 | Plant ex Wangford Arms. See also Forbes & Oulton |
| Outlaw | . | . | . | See Roosters |
| OUTSTANDING, Bury | Gtr Manchester | 2008 | . | . |
| OWL, Oldham | Gtr Manchester | 2004 | . | Moved from The Hope Inn 2006 |
| OXENHOPE MOORLANDS, Oxenhope, Keighley | W Yorkshire | 2003 | 2004 | Located at The Waggon & Horses PH. See also Oyster |
| OXFORD, Kidlington | Oxfordshire | 2002 | 2003 | . |
| OXFORD BAKEHOUSE & BREWERY, Oxford | Oxfordshire | 1984 | 1989 | Allied (Tetley) pub brewery. Formerly The Red Lion |
| OXFORDSHIRE ALES, Marsh Gibbon, Bicester | Oxfordshire | 2005 | . | Plant ex Picks. Aka Bicester Beers & Minerals |
| OYSTER, Ellenabeich, Easdale, Oban | Argylshire | 2005 | . | Relocation of Oxenhope Moorlands |