Even natural gas and solid hydrocarbons are sometimes referred to as petroleum. When petroleum first comes from the ground it is called crude oil . Later it is usually just referred to as oil . It can flow like water or be as viscous as peanut butter. It can be yellow, red, green, brown, or black.
Fractions are complex mixtures of chemical compounds that all have a similar boiling point .
Isomers are chemicals which have the same number and type of atoms but have them arranged in a different way . The huge number of possible molecular arrangements is why people talk of fractions instead of using proper chemical nomenclature. Natural Gas is a mixture of very low boiling hydrocarbons . Natural gas can only be liquefied under extremely high pressures and very low temperatures. It is also a fairly simple fraction containing mainly propane and butane .