If you are planning on keeping Oscars, then I would suggest that you think about it very carefully. If you've got a tank already, please don't rush out and buy the first Oscar you see. Step back for one minute, take a good look at your tank and ask yourself if it is big enough to house an Oscar. If you have done your research, you will know that Oscars can grow in excess of 12 inches, and they often do in captivity. Big fish require big tanks. There are two very good reasons for keeping your Oscar in a big tank. Firstly, if you house a large fish in a very small tank, you may find that you start having water quality problems. If you continue to expose your Oscar to poor water conditions, it could well have a detrimental affect on your fishes health.. Also, is it fair to restrict a large fish to a very small amount of space? Fish do need to exercise to a certain extent, so giving them enough room is only fair, don't you think?
So, exactly what size tank do you need? You won't find anything written in stone that says exactly what is needed. You don't have to go to the extremes of getting a tank as big as the one to the left, this is 300 gallons and measures 8' x 2.5' x 2.5'. However, many people seem to agree that 55 gallons is the absolute minimum for one Oscar. Personally, I would go for a 75 gallon. As for two Oscars, over 100 gallons is recommended. More than three Oscars and you are looking at an extremely large tanks with filtration to match.
My 125 gallon tank is a commercially bought aquarium. Obtaining something larger can be problematic because a lot of companies just don't stock them. However, if you do want a much larger aquarium, you may have to go down the custom made route. There are quite a few companies around that will make a tank to your specifications. There will also make the cabinet and build filtration such as sumps to fit it as well.
Oscars are adorable fish, it's no wonder that people fall in love with them. However, they do require that little bit of extra attention, so please only buy one of these fish if you know you provide it with a suitable home.