For another comparison:
A 3-inch layer of all the oil mankind has used so far would cover a mind-boggling area of 805582 square miles.
[spoil]Math:
1 gallon is 231 square inches (thus 3 in * 77)
42 000 000 000 000 gallons used.
42 000 000 000 000 * 77 = 3234000000000000 sq inches
There are 144 sq inches in 1 sq foot.
3234000000000000 / 144 = 22458333333333,4 sq feet.
There are 27,878,400 square feet in 1 square mile.
22458333333333,4 / 27,878,400 = 805582 square miles.
According to
this site, combined area of Gulf of Mexico and Hudson Bay approximately equals my calculations.[/spoil]