As you might imagine, Oxfordshire hosts conferences all the time, from academic get-togethers fervently discussing an obscure topic, to events with wide public appeal such as the Oxford Symposium on Food or the Crime Writing Conference at St Hilda's. If you're organising your own conference, here are some useful venues that between them host a diverse range of sizes and styles of gathering. They are organised by area.
If you are particularly interested in Oxford University buildings, you might like to check Conference Oxford, a website specifically set up by the University to showcase their departments, colleges and extra buildings. Many of these also feature in the below list too. NB Because of the setup of the university and the links but not ownership of colleges, while Conference Oxford is a useful starting point, you don't book the spaces through them but direct with the college or other owner.