I don't believe the OP's estimate of 52 passenger miles : 1 gallon of jet fuel is appropriate. If the OP's estimate were correct, then a mainline A320 traveling a 2000 mile distance would burn approximately:

1/52 gallon/(pax*miles) * 138 pax * 2000 miles, or

5308 gallons

Such an amount of fuel for what is nearly an LAS-IAD transcon seems rather large. Can any pilots out there weigh in?

Edit: I've found some good info on the Airbus website. The maximum fuel capacity of the A320 is 6300 gallons. Supposing that 600 gallons of fuel is held in reserve on typical transcon flights, that suggests the A320 burns about 5700 gallons when traveling at its maximum range. So, is LAS-IAD an A320's max range? Hardly! United uses the A320 on its longest transcon route, SFO-BOS, which measures 2704 miles (for instance, flight 170 on June 6, 2008).

Therefore, supposing that SFO-BOS is the A320's absolute max range (which is possible though unlikely) AND that the aircraft travels along the curved, Great Circle Mapper pathway without any deviation (impossible), then the fuel burn per passenger would be:

1/5700 gallons * 138 pax * 2704 miles, or

65 pax*miles / gallon

Of course, 65 pax*miles / gallon is conservative. Fuel burn is likely somewhere north of 70 pax*miles / gallon