I had 2 Oscars in my 90 gallon and they did fine. Plenty of space to swim. They are awesome fish. Some people call them puppy dog fish. Hole in the head is a common problem with them so its extremely important to keep the water clean with quality filters (Eheims and Powerclears) and do your weekly water changes. I also used Melafix with every water change. It smells great and in my opinion helps to keep the fish healthy.