https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft
An Airbus 380 on a long haul flight uses 3.27 l/100 km (86.39 British MPG)
I went to Australia and back in a 747-400, that does 3.76 l/100km, which is 75 MPG. That is about the same as my car does on an upcountry run, though it does around 10 MPG less locally.
The route I took to Sydney was via San Francisco, and the route back was via Kuala Lumpur, a total of 23,458 miles or 37,752 km. That works out at 1,420 litre of fuel.
That flight was for work, and was, nearly 25 years ago (where has my life vanished, I booked the flight just after 911 and got it for $400. I also got bumped off the flight, got my $400 back and an upgrade to 1st Class to KL and then Business Class to Heathrow).
Since then, I have probably driven 625,000 miles in various cars, the worse on economy was my little Corsa Automatic, it struggled to do 40 MPG (and was a lot worse around London), but all the other have easily done 50 MPG. So about 2270 lt/year, which is 5.6 l/100km.
Should have stayed in Australia.