A plant cage study was initiated to determine the residual boll weevil toxicities of the organophosphate azinphosmethyl (Guthion) and the carbamate oxamyl (Vydate) when applied in water alone or in water plus soybean oil. Mortality of boll weevils was measured immediately after spray and again at 1, 2 and 3 days after application. Oil enhanced the toxicity of both insecticides immediately after application; however, it reduced the toxicity of the organophosphate after 24 hours compared to the EC in water alone. Oil had no effect on the long term toxicity of oxamyl.