Oxford and Cambridge have different interview procedures, and even in the same university different departments have different approaches. I think that Oxford tends to conduct its interviews over 2 or 3 days, with applicants staying in college over this period, while Cambridge tends to have applicants down for just one day. I believe Cambridge often requires candidates to sit STEP papers, which are conducted externally and at a different time, while Oxford is more likely to set its own internal exams which are sat during the interview period. Both Oxford and Cambridge are flexible with their formal entry requirements, though entry standards are very high. I don't think there is much distinction in the interviews themselves. Something that many applicants coming from school struggle with is the idea that the questions are usually chosen to be a little beyond what the interviewers feel the student knows. The aim is not so much to find out how well a student has been taught but how well he or she can adapt to unfamiliar problems.