As long as they are both sexually mature, they will breed if they are male and female. However, not all Oscars will pair up with each other. From my experience, if you have a male and female only, they will pair up. You have to be sure you do have a male and female. Over the years, I have observed Oscars shovelling gravel, cleaning rocks and they have never laid eggs. Just because they do it, it doesn't guarantee you are going to have eggs come along. Try keeping your water fairly warm. Carry out a few extra water changes. My Oscars used to spawn just after water changes. Having said this, we have to go back to the fact that you may not have a male and a female.