Concentrations of about 35% CO2 and 14%E O2 where attained and maintained in a 2262 kl peanut (groundnut) silo in 3 separate experiments for periods of 48, 96, and 168 hr. Mortality of malathion-resistant Tribolium castaneum (Herbst) adults was 93.3% in cases 0.5 to 1.5 m below the surface in the 96 hr treatment. Bioassay was inconclusive in the 168 hr experiment due to malathion residue on the peanuts. Application methods and gas sampling and analyses techniques are discussed.