The two principal types of oxygen additives used in reformulated gasoline in the United States contribute little to reduce ozone pollution, says a new report by a committee of the National Research Council. In a study undertaken to examine the differences between the additives ethanol and methyl tertiary-butyl ether (MTBE), the committee found that reformulated gasoline made with ethanol is less effective, but that the overall impact of either oxygen additive on reducing ozone - a major component of smog - is very small.