A heat-effective 'integrated' process carried out in one reactor, composed of exothermic oxidative coupling of CH4 over the catalyst fixed bed and endothermic pyrolysis of naphtha injected from the outside to the stream of gaseous coupling products in the hot oxygen-free postcatalytic zone, has been studied. An additivity of the yields of ethylene formed in both component processes was examined under varied operating conditions (type of naphtha fraction, flow rate of reagents and temperature of pyrolysis). A very high degree of additivity of the yields of ethylene and its main coproducts was observed, independently of the relative contribution of the component processes to the integrated process and of applied variations in the process conditions. Evidently, the mutual interactions between the component processes and products were negligible under experimental conditions.