Obviously when discussing volumes of fuel, oil, etc. the quantity can be specified in quarts, gallons, truck-loads, etc. I personally try to specify an international measure and a US measure (e.g. kms and miles) in my answers.
However when someone asks a question requiring an answer with a specific volume, should the spelling not be "litre" rather than "liter"? Taking wikipedia as a good standard, they redirect any query for "liter" to the page for Litre. It seems silly to use the less common spelling instead of the widely used international spelling.