That's a good question! My tank holds 18 gallons, and I go through a tank a week, and that's only going to work, church, and the grocery store and back. That equals 936 gallons just for me. Of course, I'm not the only one who drives my vehicle, so that skews the results a bit. That's a lot of gas, and more money than I would like to be spending. It will be interesting to see what other answers you get.
If you check Wiki's link below, you will see that the average American drives a little over 12,000 miles a year.
There are many variables to your question:
- What kind of vehicle is driven? Car, truck or SUV
- What kind of car? Economic, Luxury, Hybrid
- Are the vehicle's tires inflated? Is the car maintained?
- What is the load of the car? How many people ride?
- Is the driver in city or highway traffic?
I would suggest that if you take an average of 25 miles per gallon, and divide that by 12,000, you get an answer of 480 gallons per person.
An "answer" that I found on-line to validate my answer can be found on the second link below, from eia.doe.gov.
The link below has some government statistics for the average number of miles people drive each year, which is probably more accurate that the 12,000 figure in Wikipedia. You will see that age and gender make a difference. The overall average is 13,476. The average for all men is 16,550 and for all women is only 10,142. Average mileage varies across age groups too.
Also, your question doesn't specify whether the "average person" is an American. The figures would be very different in many other countries. A big factor here is whether you are looking at a country with very high fuel taxes (most of Europe) or a country that subsidizes gas prices (China, much of the middle east, Mexico, etc.) since pricing has a big effect on usage.
It depends on what type of environment the people live in and what type of car a person has. These factors can change the answer very much.