Oral exams are not usually as frequents as written exams, so now I'm going to explain the opinions about this topic.
On the one hand, most teachers think that it is a good way to examine students because with the oral exam they do not have to mark written exams, they correct when the student is being examined. Even though it is a good idea, perhaps there is not enough time to examine all the students.
On the other hand, most students do not like oral exams because they do not have all the time to think about the answers and they can not delete their mistakes if they fail some questions. Some bad students hate oral exams because they can not cheat and they have to study then.
In my opinion oral exams are really better than written exams because it is a good way to learn to be relaxed when you are speaking about something important and if the subject is a language, it is good to know about your pronunciation.