Publishers
- Oresko Books Ltd. 1
- Organisation For Economic Co-Operation 1
- Organisation For Economic Cooperation And Development 1
- Oriel Press 2
- Orient Longmans 1
- Oriental Press 1
- Original Writing Ltd 1
- Orion 2
- Orion Books 3
- Orion Books Ltd. 1
- Orion Children's Books 7
- Orkney Heritage Society 1
- Ormeau Baths Gallery 1
- Orpheus Press 1
- Osprey Aerospace 4
- Osprey Air Combat 1
- Osprey Automotive 13
- Osprey Aviation 8
- Osprey Military 2
- Osprey Publications Ltd 4
- Osprey Publishing 79
- Oswald Wolff 1
- Otava 4
- Otto Schulze And Company 1
- Otto Wigand 5
- Ouest France 1
- Our Dogs Publishing Co. Ltd. 1
- Overlook Duckworth 1
- Oxbow Books 5
- Oxford Archaeology 1
- Oxford at the Clarendon Press 5
- Oxford Historical Society 2
- Oxford Illustrated Press 2
- Oxford Publishing 21
- Oxford Publishing Co 31
- Oxford University Press 368
- Oxford University School Of Archaeology 1
- Oxo Limited 2
- Oxonhoath Press 3
- Oyster Books 1
- P & O 1
- P. & G. Wells Ltd. 1
- P. Binstead 1
- P.A. Norstedt & Soner 1
- P.B.S. 1
- P.F. Volland Company 2
- P.I.C. 1
- P.M. (Productions) Ltd. 6
- P.M. Evans 1
- P.M. Evans And Son 2
- P.M. Heaton Publishing 10
- P.R. Gawthorn Ltd. 7
- P4 Spares 2
- Pacific Press Publishing Association 1
- Pacifica Press 2
- Paddington Press 3
- Pagan World Press 1
- Palace Books 1
- Paladin Press 2
- Paladwr Press 4
- Palgrave 1
- Palgrave Macmillan 7
- Pall Mall Gazette 2
- Pan Books Ltd 1
- Pan Macmillan Children's Books 3
- Pangolin London 5
- Panico Press 1
- Panstwowe Muzeum Archeologiczne 1
- Panzerwrecks 1
- Papadakis 1
- Paper Tiger 1
- Paperview Uk Ltd 1
- Paragon House 1
- Pardy & Son Ltd. 1
- Parish Pump Press 3
- Parker, Furnivall & Parker 2
- Parkgate Books 2
- Parragon 15
- Parragon Books 2
- Particular Books 3
- Partizan Press 1
- Partridge 10
- Partridge Press 1
- Partridge Publications Ltd. 1
- Past & Present Publishing 3
- Past and Present Publishing Ltd. 10
- Past Times 1
- Paternoster Press 1
- Paterson Press Ltd 1
- Paterson's Publications 1
- Pathfinder 1
- Patrick Hardy Books 1
- Patrick Stephens 27
- Patrick Stephens Limited 37
- Patterson Smith 1
- Paul Elek 2
- Paul Hamlyn 2
- Paul Harris 1
- Paul Harris Publishing 2
- Paul Mellon Centre For British Art 1