First of all, what size tank do you have? Oscars can be very territorial, and they will grow very fast. Any kind of agressive fish you add to this tank will also be territorial. I have an oscar in an 110 gallon tank, and he gets along well with the other tank-mates which are: parrot fish, irridescent sharks, silver dollars, severum, and a jack dempsey. I hope this helps. Good luck.
Tom