now i always thought the amount of fuel was based on how much was raised during the 'whip round' by passengers just before take off.
or is that just Ryanair?
IIRC a BA DC10 was despatched from one of the 'stans in the late 90s or early 2000s by such a whip round.
Edited to add: This was hearsay when I was a consultant on assignment at BA, whether it happened or not I cannot actually vouch for.