TRUE:
Gasoline or diesel fuel are petroleum based end products, thus it is oil. Water don't mix with oil and oil has the tendency to float on the top of water allowing the fuel to remain ignited. If you try to put water on a fuel fire, you would actually cause the fire to spread, because the oil is going to go immediately to the top of the water, and go where it goes. Water will only move the fuel around, spreading the fuel fire and causing more damage. Better smother the fire with something non-flammable such as a safety blanket, flour, baking soda, soil, or use a proper fire extinguisher.