A novel approach involving the use of DTA to measure quantitatively the enthalpy change during rubber atmospheric pyrolysis was developed and applied to tire rubbers : NR (natural rubber), SBR (styrene-butadiene rubber) and BR (butadiene rubber). Based on a new method of baseline determination, this approach detects precisely the overall enthalpy change during rubber pyrolysis, which consists of a linear heat capacity change, an exothermic peak and an endothermic peak. A mechanism study was carried out based on the simultaneous measurement of enthalpy and weight loss by TG/DTA. It revealed that the exothermic peak results from chemical reactions and that the endothermic peak is attributed to the evaporation of the pyrolysis products. The heats of reaction were determined to be -164, -560 and -906 kJ kg(-1), for NR, SBR and BR, respectively. The heat of vaporization varies between 170 and 200 kJ kg(-1) which is very close to the values cited in the literature for hydrocarbons. The overall enthalpy change from 30 degrees C to 510 degrees C is endothermic and is 870, 550 and 325 kJ kg(-1) for NR, SBR and BR, respectively. Using the theory of Borchardt and Daniels, the activation energies of the pyrolysis reactions were calculated to be 146, 133 and 158 kJ mol(-1) for NR, SBR and BR, respectively.