How Do I Know Which Google Account is Used for the Market?

So far I've never purchased anything from the Market but just installed free apps. Now, I'd like to purchase an app and I want to make sure the Market is using the correct Google account, since I have two (one personal @gmail.com and one from a Google Apps account for work). How can I do that? Do I just assume the first account in the list is the one used in the market? Keep in mind that I don't really remember which account I added first.