Noncatalytic oxypyrolysis of C2+-hydrocarbons from natural gas at 700-850 degrees C in the presence of steam and limited oxygen yields ethylene and propylene with appreciable conversion and high selectivity but with almost no coke or tarlike product formation. In this process, the exothermic oxidative hydrocarbon conversion reactions are coupled directly with the endothermic cracking of C2+-hydrocarbons by their simultaneous occurrence. Hence, the process operates in a most energy-efficient and safe (or nonhazardous) manner and also can be made almost thermoneutral or mildly endothermic/exothermic, thus requiring little or no external energy for the hydrocarbon conversion reactions.