The "crude oil" pumped out­ of the ground is a black liquid called  . This liquid contains aliphatic hydrocarbons, or hydrocarbons composed of nothing­ but hydrogen and carbon. The carbon atoms link together in chains of different lengths.

It turns out that hydrocarbon molecules of different lengths have different properties and behaviors. For example, a chain with just one carbon atom in it (CH₄) is the lightest chain, known as methane. Methane is a gas so light that it floats like helium. As the chains get longer, they get heavier.

The first four chains -- CH₄(methane), C₂H₆ (ethane), C₃H₈ (propane) and C₄H₁₀ (butane) -- are all gases, and they boil at -161, -88, -­46 and -1 degrees F, respectively (-107, -67, -43 and -18 degrees C). The chains up through C₁₈H₃₂ or so are all liquids at room temperature, and the chains above C₁₉ are all solids at room temperature. So what's the real chemical difference between gasoline, kerosene and diesel? It has to do with their boiling points. We'll get into that on the next page.

Reference

http://arabian-chemistry.com/ماهو-الفرق-مابين-الغازولين،-الكيروسي/­