The ancient tuning was four strings, tuned in fourths ADGC--And that is still basic, more or less, with a lot of variations for additional strings. The standard Arabic tuning is DGADGC The Turkish/Armenian cabaret players used EABEAD for years, but apparently have moved away from it.

I don't pretend to be an expert, but here is a link from the above list, to an article at Lark in the Morning written by someone who knows about it.
Tunings Article by David Brown

I tried to learn oud once, but ended up with a very poor quality instrument, and, beyond that, had trouble making up my mind which type of music I was interested in, and just got bogged down.