Composition of oil gas is CH₄ = 25-30%; H₂ = 50-55%; CO = 10-12%; CO₂ = 3%

It calorific value is 4500-5400 kcl/m³. It is used as laboratory gas.

Oil gas is prepared by thermal cracking of mineral oil, like kerosene oil.

                     _cracking

C12H26               H₂ + CH₄ + C₂H₂ + C₂H₄  + C₂H₆  + C₃H₆  + CO + CO₂ +  C

^{Kerosene oil}

The cast-iron retort is heated to red-hot. The kerosene oil is allowed to fall dropwise on the red hot retort. It gets cracked to form lower hydrcarbon mixtures. These gaseous mixture passes through the bonnet covert to the hydraulic main where tar gets condensed. The extent of cracking can be tested by the colour of the gas (should be golden yellow) at the testing tap.

The gas is collected and stored in gas holders.