While on our SAS flight from Longyearbyen to Oslo, we browsed the SAS magazine airplane descriptions and it contained fuel burn per seat in litres for each fleet type.
SAS operates the 319/320/321 and 737-600/700/800. Seating is as follows:
SAS reports a mere 0.001 difference in fuel burn per seat per kilometer in litres in favor of Boeing in each case–despite the 738 having 18 more seats, in which case the difference could be expected to be much greater.
We found the data to be quite illuminating.
Fuel burn per seat per km, in litres: