| Oakham Ales | http://www.oakhamales.com |
| Oakleaf Brewing Company Limited | http://www.oakleafbrewing.co.uk |
| O'Hanlons | http://www.ohanlons.co.uk/ |
| O'Hanlon's Brewing Company Ltd | http://www.ohanlons.co.uk |
| Okell & Sons Ltd | http://www.okells.co.uk |
| Old Bear Brewery | http://www.oldbearbrewery.com |
| Old Cannon Brewery Ltd | http://www.oldcannon.co.uk |
| Old Laxey Brewing Co | |
| Old Luxters Farm Brewery | http://www.chilternvalley.co.uk |
| Old Mill | http://www.oldmillbrewery.co.uk/ |
| Old Mill Brewery | http://www.oldmillbrewery.co.uk |
| Old Spot Brewery Limited jp.hargreaves | |
| Old Wheelton Brewery dressers.arms | |
| Oldershaw Brewery | http://www.oldershawbrewery.com |
| Organic Brewhouse | http://www.theorganicbrewhouse.com |
| Orkney | http://www.orkneybrewery.co.uk/ |
| Orkney Brewery | http://www.orkneybrewery.co.uk |
| Otter | http://www.otterbrewery.com/ |
| Otter Brewery Ltd | http://www.otterbrewery.com |
| Oulton Ales Ltd | http://www.oultonales.co.uk |
| Owl Brewing Co Ltd | http://www.owlbrew.co.uk |
| Oxfordshire Ales bicesterbeers |