In flame ionization detection of hydrocarbons, many parameters affect the carbon response of the detector for sample hydrocarbons relative to the calibration hydrocarbon. This report discusses the effect of the hydrogen‐to‐diluent ratio of the detector fuel on the relative carbon response; The response of a typical flame ionization detector to methane, acetylene, ethylene, benzene, and toluene relative to propane is presented for fuels of varying hydrogen percentage in helium and in nitrogen.