Generally bitumen is categorized under two main groups as follows:

• Petroleum Bitumen:

The source of #petroleum bitumen is crude oil.  Crude oil is transported to the refinery by pipe.  There the crude oil is separated to its component by a #distillation process.  One of the resulting products is petroleum bitumen.  In other words petroleum bitumen is produced from crude oil directly or with some additional processes such as #air_blowing.  As a matter of fact petroleum bitumen is a #residue of the distillation tower.  The content of bitumen in crude oil is various from zero to more than fifty percent, moreover petroleum bitumen from various sources have different specifications.  As a result crude oil with good quality leads to petroleum bitumen with a better quality.

• Natural Bitumen:

This kind of bitumen is found in nature directly.  #Natural bitumen does not require the distillation process.  As a matter of fact the source of #natural_bitumen is crude oil too, but volatile materials of the crude oil have evaporated over the years and oxidization and polymerization process has been done.

Natural bitumen is not found in its pure state in nature.  It almost certainly contains some impurities and inorganic materials that it is called #asphalt.  There are three kind of natural bitumen as follows:

#Rock_Asphalt, #Lake_Asphalt and #Gilsonite.

The most pure natural bitumen is called Gilsonite. Gilsonite has more than 90 percent bitumen.