Formation of kerogen
Type I: Sapropelic
- containing alginite, amorphous organic matter, cyanobacteria, freshwateralgae, and land plant resins
- Hydrogen:carbon ratio > 1.25
- Oxygen:carbon ratio < 0.15
- Shows great tendency to readily produce liquid hydrocarbons.
- It derives principally from lacustrine algae and forms only in anoxic lakes and several other unusual marine environments
- Has few cyclic or aromatic structures
- Formed mainly from proteins and lipids
Type II: Planktonic
- Plankton (marine)
- Hydrogen:carbon ratio < 1.25
- Oxygen:carbon ratio 0.03 to 0.18
- Tend to produce a mix of gas and oil.
- Several types:
- Sporinite: formed from the casings of pollen and spores
- Cutinite: formed from terrestrial plant cuticle
- Resinite: formed from terrestrial plant resins and animal decomposition resins
- Liptinite: formed from terrestrial plant lipids (hydrophobicmolecules that are soluble in organic solvents) and marine algae
Type II: Sulfurous
Type III: Humic
- Land plants (coastal)
- Hydrogen:carbon ratio < 1
- Oxygen:carbon ratio 0.03 to 0.3
- Material is thick, resembling wood or coal.
- Tends to produce coal and gas (Recent research has shown that type III kerogens can actually produce oil under extreme conditions) 
- Has very low hydrogen because of the extensive ring and aromatic systems
Type IV: Residue
Origin of material
- Ocean or lake material often meet kerogen type III or IV classifications.
- Ocean or lake material deposited under anoxic conditions often form kerogens of type I or II.
- Most higher land plants produce kerogens of type III or IV.
- Some coal contains type II kerogen.
- Carbonaceous chondrite meteorites contain kerogen-like components.Such material is thought to have formed the terrestrial planets.
- Kerogen materials have been detected in interstellar clouds and dustaround stars.[14