It varies a LOT, however, an interesting similar topic.
I have had experience with two (2) women who would come just giving me oral.
No stimulation by me whatsoever, they were just so into giving head that they would orgasm from the experience.
Interestingly, both are from the UK (one Scottish, the other English)
Both are blondes.
Both are nurses by profession.
Both were beyond multi orgasmic. To be honest with you, it was a bit much at times. I would not be exagerating to say that in one session, they both could come 20 or 30 times easily.
The one thing I do remember that the one girl said to me was, "I love sucking willies".
That one will stay with me for the rest of my life.