In addition to chemical composition fuel gas may need to comply with parameters such as calorific value, Wobbe index, dewpoint, etc. The following specification is for the British National Transmission System.

Incomplete Combustion Factor (ICF) - an empirical index that relates the composition of a gas to its tendency to burn incompletely in a gas appliance. Dutton defined the ICF as: ICF = 0.64 × (W - 50.73 + 0.03 × PN) where W is the Wobbe index, MJ/m³; PN is the volumetric