Let's make sure we are all on the same page first:
Oral sex means someone's mouth comes in contact with another person's genitals (vulva, vagina, clitoris, anus, perineum, penis, scrotum, (and sometimes breasts and nipples).
Here's another reason condoms are great and save lives. They come in flavors, can be cut to cover a vulva or anus if a dental dam is not around, and it creates a barrier between a person's mouth and the genitals of their partner(s).
The Center for Disease Control has created a new fact sheet on Oral Sex. Check it out for information about transmission of HIV and other Sexually Transmitted Infections (STI).