Most oral exams I've been to have been either a) talk about a report you've written, or b) draw 1 of x (say 8) subjects that have been covered throughout the ye

Most oral exams I've been to have been either a) talk about a report you've written, or b) draw 1 of x (say 8) subjects that have been covered throughout the year, and do a presentation on it, usually with 20-30 minutes preparation. All subjects have of course been published at least 2 weeks prior to the exam. So I don't see a problem with telling "what to expect", but I do see a problem with 1 professor and one censor examining 300 students for for 30 minutes each.