Well I am surprised an American has heard of litres, I doubt very much if many people outside the US give much credence to a US gallon, the US might be big but it ain't that big, as it is currently finding out! All the boxes I look at (and I am in Thailand mostly far eastern products, pretty neutral ) quote US gallons and Imperial gallons and litres on the box so don't be fooled that the rest of the world is as ill informed as the US consumer.
Actually, there was a big push by the government about 25 years ago to switch to the metric (is that the proper name) unit of measure. Most all the gas pumps were switched to liters. I didn't have a clue how much I was paying for a gallon of gas and felt like the gas stations were ripping everyone off. There was such backlash from it that everything changed back to the old way. The government is still trying to switch some thing over. About 19 years ago, they made it where any construction that had government money in it (schools, etc) had to be metric. The block company I worked for at the time had to switch their block machines over to make 400x200x200 unit instead of the regular 16x8x8 unit. Anyway, the simple thing to do is ask someone if they mean US or UK. I still think that 99%, even those outside the US, will say US gallons.
20 some odd years later and we are still measuring by the old ways 
They use the metric system.
/www.know-britain.com/general/common...countries1.html 
