Water is around 25 percent heavier than gasoline which is 25 percent lighter than water of the same volume and gallons.
A gallon of water weighs 25 percent more than a gallon of gasoline.
Water weighs around 8.4 lbs per gallon.
A gallon of gasoline weighs 6 lbs even though they are both liquids.
The reason for water weighing more than gasoline is water is denser than gasoline.
The water is denser than gasoline so there essentially more molecules of water in a given volume.
For example in a given volume, there may be 15,000 molecules of gasoline but 20,000 molecules of water.
Water is also heavier than diesel which is why water settles at the bottom of a diesel tank and even a gasoline tank.
Diesel fuel is much denser than gasoline.
This means that there is more mass in the same volume.
Because diesel fuel is about 14 percent heavier, there is approximately 14 percent more energy in a gallon of diesel fuel vs. a gallon of regular gasoline.