This paper deals with a new method to calculate the higher heating value (HHV) of pyrolysis oils by using the analysis results of their gas chromatography-mass spectrometry or high-pressure liquid chromatography. This new method is called ''GC-MS method'' or ''GCM''. The HHV which is calculated by this method is compared to the one given by the researchers (generally obtained by bomb calorimeter) on the one hand and those of Dulong's and Vondracek's formulae on the other hand. The results show that GCM and Vondracek are generally in a good agreement with the experimental values than those obtained with Dulong's formula.