Two versions of a zero-dimensional heat release model have been utilised to compute the mass of the gases in the burned zone in a two-stroke gasoline engine for which measured pressure -crank angle data were available. The two sets of the mass fraction burned profiles, obtained for 10 different engine operating conditions, showed satisfactory behaviour. The model results contain useful informations about the combustion phenomena occurring in the engine which otherwise are difficult to measure. In addition, the gas exchange parameters were also known from the computed results. Such model results will certainly be an asset to an engine designer. The model, consisting of only algebraic equations, requires very small computer time and thus, can be integrated with a computer based data acquisition system to monitor the mass burning behaviour on a real time basis.