How much does one gallon of crude oil weigh?

According to the NYMEX, light sweet crude (the grade of oil most commonly traded in the commodities markets due to its comparable low level of difficulty in gasoline distillation) has an API gravity of 34 degrees to 41 degrees for foreign delivery.

The API gravity is a scale developed by the American Petroleum Institute. The formula is to calculate SG at 60 degrees F = 141.5 / (API gravity + 131.5) which translates to between 0.855 and 0.820 (per liter)

A gallon is equivalent to 3.785 liters, so the answer is:

Between 3.104 and 3.236 kg (7 lbs) per gallon of light sweet crude.