(a) Crude oil is extracted from the Earth's airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous. It was formed from the remains of marine airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous which lived millions of years ago. The airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous fuels airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous, oil and natural airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous have reformed by the action of heat and airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous over millions of years, in the absence of airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous, on material from animals and plants (organic material) which has been covered by layers of airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous rock.

(b) Crude oil is a airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous of a very large number of compounds. A mixture consists of airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous or more elements or airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous not airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous combined together. The chemical properties of each substance in the mixture are airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous. This makes it possible to separate the substances in a mixture by airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous methods including distillation.

(c) Most of the compounds in crude oil consist of airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous made up of hydrogen and carbon atoms only and are called airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous. They can be separated into fractions, each of which contains molecules with a airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous number of carbon atoms, by airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous the oil and allowing it to condense at a number of different airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous. This process is airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous.

(d) The hydrocarbon molecules in crude oil vary in airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous. The larger the molecules the airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous the number of carbon atoms in the hydrocarbon, the airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous its boiling point, the airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous volatile it is, the less easily it flows i.e. the more airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous it is, and the less easily it ignites, meaning the less airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous it is, and this limits the usefulness of large hydrocarbon molecules as airchemicallycoalcompoundscrustdistillationevaporatingflammablefossilfractionalfuelsgasgreaterhigherhydrocarbonslessmixturemoleculesorganismsphysicalpressuresedimentarysimilarsizetemperaturestwounchangedviscous.