The gasoline that you put in your petrol motor is C_5H_12 to C_7H_16, a mixture of the isomeric pentanes and hexanes, and a few heptanes. The gas that you put in your diesel motor has one degree of unsaturation, i.e. C_6H_12 to C_10H_20; with the possibility of geometric isomerism, diesel is a bit of a witches' brew.
Most of the time, when we want to represent gasoline, we would use the formula C_6H_14, i.e. hexanes; and of course hexanes could be a mixture of isomers: "dimethylbutanes"; "ethylbutane" "methylpentanes"; and "n-hexane".
In the laboratory, often we use so called "petroleum ethers", with various boiling point ranges, 40-60 ""^@C, 60-80 ""^@C, 100-120 ""^@C. These tend to contain some unsaturated material.
