* Composition: Petrol is a blend of different hydrocarbons (molecules made of hydrogen and carbon) with varying chain lengths. These hydrocarbons are extracted from crude oil and then refined to produce gasoline.

* Variable Composition: The exact proportions of these hydrocarbons can change depending on the source of the crude oil and the refining process. This means that petrol from different sources or refineries might have slightly different compositions.

* Separation: The components of petrol can be separated by physical means like distillation. This wouldn't be possible with a compound, which has a fixed chemical composition.

In contrast, a compound is a substance formed when two or more elements chemically combine in a fixed ratio. Water (H₂O) is an example of a compound, always consisting of two hydrogen atoms and one oxygen atom.