The validity of the commonly used flame marker for heat release rate (HRR) visualization, namely the rate of the reaction OH + CH2O ⇔ HCO + H2O is re-examined. This is done both for methane–air and multi-component fuel–air mixtures for lean and stoichiometric conditions. Two different methods are used to identify HRR correlations, and it is found that HRR correlations vary strongly with stoichiometry. For the methane mixture there exist alternative HRR markers, while for the multi-component fuel flame the above correlation is found to be inadequate. Alternative markers for the HRR visualization are thus proposed and their performance under turbulent conditions is evaluated using DNS data.