Hi, I was wondering about what size of tank I need for an oscar. My dad saw one in the store and he fell head over heals for the type of fish. I haven't bought one for him yet because I need info about tank size so that I can know whether or not I have a tank that would work (if it isn't already filled with goldfish or a betta:)

oscars are aggressive fish, they probably need more than 10gallon, they get big. try this forum; http://www.oscarfish.com/

Minimum 50 gallons. 75 gallons is recomended. lol This question was asked not long ago on another forum. They are really small in the pet shops but get huge very very fast. And they live for like 15 years. They get about a foot long, Id compare them to the size and shape of an American Foot ball. They need tank space. And lots of it.
Like goldfish, and probably even more so, oscars are messy, they are messy eaters, produce excess slime and create a huge bioload. So the filter needs to be 10 x the gallonage.
And they are not really that agressive, one of the more docile cichlids, however, be every careful when choosing tank mates, as they are still agressive fish, and dont like other fish getting into their space. (Need plenty of space) I find they get moody, they have very grouchy moments. They are on of my fave types of fish, and if i had the room for a tank that size id have one, or 10 lol. - Meg

Yup, I would probably have a 160 gal tank with one oscar, with about fluval 4+ filters I think I might be exaggerating, but trust me, large cichlids like oscars are messy, and they will certainly need more than one filter
EDIT: whoops! sorry Meg_carrol, I didnt know you already said that