is it true that oscars like all tankmates, so long as they are tasty??
Well that and they fit into their mouths!
The thing with Oscar is that they are not very aggressive as far as these types of cichlids go. They are generally laid back and take well to other tankmates, minding their own for the most part. There are always exceptions, and more and less aggressive then usual within all species.
The thing is I'm recommending no tankmates not because they can't get along with other fish, but because they are huge, messy fish. There is simply no room in a tank this size. There is no room for 3 Oscars in a tank this size either. A pair of them will fill it up and more.