How much fuel does an international plane use for a trip?
A plane like a Boeing 747 uses approximately 1 gallon of fuel (about 4 liters) every second.
13.5 hrs = 48,600 seconds, so on a 13.5 hour flight a 747 can be expected to use around 48,600 gallons of fuel. At $1.50/gallon for jet fuel (I heard that figure somewhere else on FT), the 747 will burn about $72,900 worth of fuel.
Divided by 300 passengers, that's $243 per person in fuel costs.