What are the chances of getting pregnant if a condom isn't used?

Quite high

If a full ejaculation occured INSIDE the vagina, then there is a definite risk.

Ejaculating outside drasticly decreases that chance, altough people will bash your skull in by claiming it is equaly dangerous because of "precum" or preejaculatory fluid. Still, less sperm mean less chances (any protection is better than no protection).

Still, I recommend condoms because of STD risk's involved in sex.