Vacation Residence

While Oxford do accommodate you in your first year, that's only during term time. The colleges use student rooms over the vacations (Oxford jargon for the time between terms). This makes them money (and keeps your rent down) and also lets them accommodate interview candidates in December. So if you live in college accommodation, you normally have to move out three times a year. However, some colleges offer what is known as vacation residence, where you may stay in your room even out-of-term.

College	Vacation Residence
Brasenose	Unknown
Corpus Christi	Unknown
Exeter	Unknown
Harris Manchester	Unknown
Jesus	Second and third years can stay in their accommodation all the academic year round, including holidays. First years living in college can apply to stay, and the cost per night will be £21.80 from next year. Conference guests can prevent requests being granted. It's easier for internationals. We also have a scheme where you can claim back 17 nights worth of vacation residence if you need to stay in Oxford for any academic reason.
Magdalen	Unknown
Oriel	As long as you have a good reason (exams, project work, international and can't go home, revision the term before finals, etc), then it's fairly easy to get a room. At certain times of year, e.g. around interviews, you may have to move rooms and possibly to JMH. When selecting your room you will be told whether it is 'tagged' (needed for conferences and so you would have to move rooms if you stay). If staying for academic reasons, vacation grants can give you about 50% off for 15 days per year.
Queen's	It is relatively difficult to stay at Queen's during the vacations, though it is sometimes possible (e.g. just before term starts; or if you're an international students; or for final year students over Easter).
Regent's Park	Vacation residence can be provided, subject to availability. Generally, all finalists can stay in College over the Easter vacation. The cost is the same per-nightly rate as during term. There is a grant/support fund to help finalists cover the cost of vacation residence.
St Anne's	Unknown
St Hugh's	College tries to dissuade people from staying over the holidays. But if you genuinely need to stay in college it should still be easy. There's a reasonably high chance you'll be forced to move to another room which can be annoying. Students are negotiating with college over the system.
St John's	Unknown
Trinity	Vacation rent on-site is £22 per night (in 2014) but some halls are unavailable due to conferences and it is completely unavailable during the middle of summer due to a summer school. However, accommodation in North Oxford is generally always available, costing £16 per night.
Wadham	It costs around £18 a night. It is fairly easy to stay, although lots of people are required to move rooms, which is especially frustrating when you're staying for exams. The main issue is that it's very expensive to stay the whole vacation - and there's no food included so it's much more costly than during term time.
Worcester	Vacation residence grants are available for undergraduates who need to be in Oxford during the vacation to do academic work which could not easily be done at home. If students do not have a vacation residence grant, they can stay in College during the vacation for £19 a night (subject to room availability).

For more help choosing a college, you might like to try the College Suggester tool.