By simultaneous reactions of methane with CO2 and O-2 over NiO-CaO catalyst under certain reaction conditions, it is possible to convert methane into syngas with low H-2/CO ratio (1 < H-2/CO < 2) at above 95% conversion, with 100% CO selectivity and above 90% H-2 selectivity and also with very high CO productivity without catalyst deactivation due to coking for a long period, in a most energy efficient and safe manner, requiring little or no external energy.