I always assumed it was pronounced "O.S. ten", but today I heard a girl call it "O.S. Ex". I started laughing repeating "O.S. Sex"? The she tells me "Yeah, that's the way it'S said in English", being French I really could not argue much with her cause I must admit I haven't heard it very often said aloud in English (maybe a few times on TEch TV, but I'm pretty sure they call it "O.S. Ten". Anyway, I have serious doubts that she is right.
So, is it "O.S. ten" or "O.S. Ex" (OS Sex)? 