I can JUST get the door shut with a 5lb tank. I think there have been people who have fit a 10lb in there, but you need to remove the interior door panel (with the shelves, etc) and replace it with a flat panel (I've seen dry-erase board used). Too much of a PITA for me, so I just use a 5lb. In fact, I prefer having 2 5 lb tanks rather than 1 10lb tank. Given that you rarely know when a tank is almost empty, and that they always seem to cash out on a weekend when the welding shop is closed, I like having the ability to just switch them out when one dies, then filling the other one come monday.