Verbal refers to something expressed or transmitted in speech or something associated with words. Oral refers to something that is spoken rather than written or something pertaining to the mouth. While verbal refers of an association with words, in everyday usage it has come to mean expressed or transmitted in speech. However, to be precise and correct, we would say an oral exam, an oral contract etc.

"Verbal" can mean "with words". "Oral" means "with speech". Verbal communication: communication with words/writing. Oral communication: communication with speech/spoken word.