We basically have to wear gowns to all official university or college meetings. This includes university exams, college collections, vivas, principal's collections (termly report-reading with prinicpal), any meeting with university officials, on any occassion when the chancellor or vice chancellor is present (eg. matriculation, graduation, attending Chris Patten's speech to the Oxford Union), and formal hall. There is also a university regulation which stipulates that gowns must be worn to lectures, but this has largely lapsed in recent years. I only have one lecturer who wears a gown to give lectures, and gets annoyed when others don't wear theirs'. For all the above-mentioned events the wearing of gowns only is required. However, for matriculation, university examinations and graduation, sub fusc must also be worn (for women white shirt, black skirt/trousers, black tights, flat black shoes, black ribbon tie, mortar board. For men, white shirt, black suit, black shoes, white bow tie, mortar board). On average I wear my gown once or twice a week depending, and this year I am anticipating wearing sub fusc on four occassions.