i have always thought my 2 oscars were the same sex..
recently i got interested in trying to see how to find out what their sexes were. after reading that they all look the same, i started to read up on breeding and the mating rituals.
i put in a flat rock and have been noticing the locking of the jaws, shoveling the gravel, cleaning the flat rock etc.
could this be because they are the same sex and both "ready" to lay / fertilize eggs, or is it more likely i actually have a male and female?

fingers crossed i get some eggs

welcome to the site

Firstly, approximately how old are you Oscar's. The behavior you describe would be expected if you had a breeding pair. However, from my experience, it certainly isn't a foregone conclusion that you have a breeding pair, some Oscars will go through this behavior & never lay eggs. A female Oscar can produce eggs on her own without a male present, although they obviously will not be fertilized.

The next time they are really going for it, have a look at the underside, see if anything is sticking out, a small spike, or maybe a slightly oval protrusion. This could give you an indication of whether you have a male or female, or if they are going to start breeding.

one of them is about 2 and have had since it was tiny, i bought the other one when it was already fully grown and i have a feeling it could be pretty old..

it was only about 4-6 months ago when the younger of the two had that white lump/pimple looking thing on its bottom lip.
is that a sign that he/she is now ready to mate?
i read something about it but cant remember if they had a reason for it occurring

Some people think the bump under the chin is from digging and moving gravel. Some oscars get it and some never do.

Oscars sexually mature at around 16 months old.

Sounds like you might have a pair there, fingers crossed for ya mate

If they are two years old, then they are definitely sexually mature. As for the pimple on the chin, this is something that is quite common on Oscars. A fish of 4 to 6 months old is not sexually mature so I don't think we can relate the pimple to them becoming sexually mature. I think it would be a case of studying Oscars for quite a long period of time, maybe then you could relate this pimple to either breeding, or just something that happens naturally to some fish. However, it does rather seem strange that the pimple is in the exact spot that they use to clean the rock, it is something that has always intrigued me.