A kind of fuel · also called diesel, petrodiesel, diesel oil, DERV

About
Diesel fuel is an engine fuel that is slightly lighter than water, packing significant chemical energy into every gallon.
Diesel fuel has a typical density of around 7.0 pounds per gallon (0.84 g/mL). Because it is less dense than water, it floats on top of water if spilled. It is heavier and denser than standard automotive gasoline, but it remains lighter than most household cooking oils.
From Wikipedia
Diesel fuel, also called diesel oil, fuel oil (historically), or simply diesel, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place as a result of compression of the inlet air and then injection of fuel without a spark. Therefore, diesel fuel needs good compression ignition characteristics.
Read more on Wikipedia →Text from Wikipedia’s “Diesel fuel” article, CC BY-SA 4.0.
One cup weighs
7.01 oz (199 g)
Quick answer
One US cup of diesel fuel weighs about 7.0 ounces (199 g). This makes it roughly 16 percent lighter than an equal cup of plain water.
Typical figures, the same ones every comparison on the site uses; real ones vary.
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Next to anything: a person, a car, another fuel.