Read somewhere you should never let your tank get below 1/4 nor should you fill it over 3/4 of a tank...I do understand the 1/4 part but do not know what they meant by the never over 3/4 bit...?? Anyway, I never let mine get below 1/2 to 1/4 anyway but I do fill it to the top despite what they say. Filled up two days ago at the really economical price of $3.19 per gallon...Yikes!!!