Abstract: A compact instant steam generator is provided for on site use where various qualities of steam may be required. A water jacket cooled combustion chamber having a burner at one end and a water spray nozzle at the other end is used. In operation, a water spray is directed countercurrently to the burner exhaust gases whereby instant vaporization of the water occurs due to the extreme turbulence and thorough mixing of the opposing streams. The water spray is located remote from the burner flame so that flame quenching by the water does not occur. The device of the invention is capable of generating steam while coproducing a very low level of carbon monoxide.