I think the mentality that condition A is much better than condition B so if we don't give our fish with the best home possible is total hooey. Sorry if that too sounds harsh but I don't think a 30"x18" footprint is appropriate for an oscar, even if it has "maxed out" at 10 inches. If you can't provide the minimum tank requirements necessary than you shouldn't be keeping the fish.
To the OP...there is a lot of misinformation out there. You've already shown that you're going to try to go above and beyond the bare minimum by purchasing a larger tank than what you read was appropriate, and I applaud you for that. However, it would be best to look for a tank with better dimensions. A 75g is the minimum I'd keep an oscar in and I bet many would agree. You should not have to pay an exorbitant amount...just keep checking places like Craigslist for deals.
To the OP...there is a lot of misinformation out there. You've already shown that you're going to try to go above and beyond the bare minimum by purchasing a larger tank than what you read was appropriate, and I applaud you for that. However, it would be best to look for a tank with better dimensions. A 75g is the minimum I'd keep an oscar in and I bet many would agree. You should not have to pay an exorbitant amount...just keep checking places like Craigslist for deals.