Abstract: Apparatus and method for improving the efficiency of combustion, particularly in internal combustion engines, are disclosed. Air is circulated at a substantially constant, controlled rate from a blower or compressor through a control valve to a plurality of release points beneath a catalyzing or catalyst-forming liquid, such as water, and is released in such a manner as to ensure the slow growth of relatively large bubbles. These bubbles break at the liquid surface, and the catalyst-laden air is then returned to the gas impelling means, e.g. blower or compressor, in which it is mixed with more air and returned to the system. A portion of the catalyst-laden air is directed to the combustion device, e.g. the carburetor or intake manifold of an internal combustion engine, the remainder being returned to contact with the catalyzing or catalyst-forming liquid.