Crude oil is a fossil fuel - what is a fossil fuel and how is crude oil separated into its fractions?

A fossil fuel is a substance like coal, oil, or natural gas formed from decayed plant or animal remains which can be burned to produce energy and power. Crude oil is separated by fractional distillation - first you need to heat it to evaporate the hydrocarbons. The vapours enter the column which is warmer at the bottom and cooler at the top, the different fractions of crude oil will condense at different temperature levels of the column as they have different boiling points.