Oscar's need 72"x 20"+ IMO. they can and will reach 15" if given the chanceIMO get a 6 foot tank and get a JD and Oscar and some other smaller cichlids. You will get bored with only 2 fish in tank. I mean sometimething with a 48x18 footprint is the bare minimum for an oscar and a JD imo but that's really pushing it as an oscar needs a 48x18 tank to itself, also it's not really about gallons, it's about footprint of the tank.