Oxygen is often the rate-limiting factor in aerobic in situ bioremediation. This paper investigates the degree to which air or oxygen gas can be emplaced into the pore space of saturated porous media and provide a significant mass of oxygen. Column experiments were performed to test three emplacement methods: direct gas injection, injection of water supersaturated with gas, and injection of a hydrogen peroxide solution. The direct gas injection method fills 14--17% of the pore space with trapped gas. Water supersaturated with gas fills 18--27% of the pore space with a trapped gas phase, and hydrogen peroxide solution injections emplaces trapped gas in 17--55% of the pore space. In addition to supplying oxygen, gas entrapment causes a decrease in hydraulic conductivity which could be an advantage by decreasing the flow of contaminants offsite. The relative hydraulic conductivity of porous media with a trapped gas volume of 14--55% was 0.62--0.05. ¿ 1997 American Geophysical Union