On the Cichlid aggression scale of 1-10 I think Oscar's rate about......4-5. The reason I say that is when put up against actual aggressive fish such as Green Terrors, Jack Demseys, Midas, Flowerhorn, Jaguars & Convicts the Oscars will usually lose every time. Unless you introduced one of those other fish as a juvie and the Oscar was already full grown. Now with other Oscars & other fish that will allow themselves to be pushed around (key words), then yes-Oscars may 'seem' aggressive. They're territorial and they'll bully another fish
if given the chance but as far as "real" aggression? Not so much. I know people keep JD's and Oscar's together, I think it's a roll of the dice. I've got an Oscar with a Green Terror but the Green Terror is FAST & was a juvie when introduced. My other 4 Oscars have another Oscar as their tankmate and get along wonderful. But getting 2 Oscars to get along is a roll of the dice in itself. I can't remember what size your tank is, but keep in mind Oscars get 12"-15" long and they're very bulky/thick fish. An Oscar needs a minimum of 75 gal bio-load wise and territorial-wise. Some people claim a 55 g minimum but my opinion is that's just not big enough for such a long bulky fish.
These are my thoughts and opinions and I'm not going to argue or defend them-sorry

. I've got 5 super healthy active Oscars though and that's good enough for me.