Silly Cash on Board question

[cruisincountrygirl]

I imagine I likely know the answer to this, but I'm going to ask it anyway, just to be sure. We are leaving very shortly for Barcelona for a cruise around the Mediterranean. Admittedly, I'm a little OCD, and we set a budget when we travel, allotting a certain amount of money for each day.

Is my understanding correct that all the Carnival ships operate in dollars when on board, or is that just stateside and cruises leaving the states?

I want to be certain that I do the currency conversion to keep us on budget for ship purchases, etc. I was assuming they do use USD, but you know what assuming does for you. . . ;)