Composition of Crude Oil
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The table below gives the names, fraction of the total, and approximate molecular size of crude oil fractions.
| fraction | no. carbons | b.p. | % (*) |
|---|---|---|---|
| Gases | 1-4 | <0 | 2 |
| Light Naphtha | 5-7 | 27-93 | 34 |
| Heavy Naphtha | 6-10 | 93-177 | |
| Kerosene | 10-15 | 177-293 | 11 |
| Light Gas Oil | 13-18 | 204-343 | 21 |
| Heavy Gas Oil | 16-40 | 315-565 | 31 |
| Residuum | >40 | >565 | |
| (*) percentage composition for Gippsland Crude Oil | |||
Some of the interesting and gluggy compounds found in crude oil are shown below; in the first three, a common chemical shorthand for drawing carbon skeletons is introduced - unless shown otherwise, everything is assumed to be a carbon substituted with as many hydrogens as it can manage.
 substituted cyclopentane, cyclohexane, bicyclic species |
 substituted aromatics - xylene, naphthalene, perylene |
 thiophene, elemental sulfur, nonyl mercaptan |
 substituted pyridine, pyrrole, carbazole |
 phenol, long chain alcohol |
The composition of crude oil varies greatly from one source to another- crude oil from the Middle East contains a greater proportion of straight chain hydrocarbons, while Nigerian crude oil is predominantly cyclic hydrocarbons and aromatics. Mexican crude can be up to 5% sulfur, while Pennsylvanian crude contains less than 0.1%.
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