Before I updated my macbook pro was running on whatever OS it had when I bought it four years ago. It was the one before snow leopard I think. It ran RCT3 perfectly fine and I never had a problem. Now that I've updated to Maverick it won't open the game anymore. I'm using an actual DVD that I insert into the computer rather than a download if that makes a difference. I haven't tried to reinstall the game or anything yet either.