Oscars are fine alone, they aren't really social and will interact with they're owners. They're territory will go beyond the tank walls and they each have their own personality. They are also trainable and some even enjoy being pet. many regard them as the most intelligent aquarium fish.
The downside is they will destroy live plants, and are clumsy. So careful selection of decorations without sharp points, and driftwood. They do best with a filter that has a bio wheel, and no under gravel filter because it's been known to cause HITH, a horrible disease that creates large holes in the poor fishes head. Photo http://i54.tinypic.com/2mwrtc1.jpg
"The major portion of a wild Oscarís diet consists of insects and crustaceans such as freshwater shrimp and crawfish. Oscars are not piscivores (carnivorous animals which eat primarily fish.) Fish actually comprise a minor portion of their diet. Oddly enough, the primary fish prey of Oscars in the wild are catfish. Keep that in mind when selecting tankmates.
Nor are Oscarís carnivores (animals which eat only meat.) In the wild, a significant component of an Oscarís diet is fruit that has fallen into the water. As a result, Oscars have a high dietary requirement for Vitamin C.
In addition to fruit, a significant component of a wild Oscarís diet consists of algae and green plants. Not because they seek out these foods and eat them, but because these are the gut contents of their prey. "
My parents used to have one :)