A measure of the thermal conductance of the plumage of normal and oiled ducks was determined from regression analyses that related metabolic rate and ambient temperature. The heat loss of heavily oiled mallards and scaup was 1.7 and 2 times greater than their normal values, respectively. Oiling not only tended to increase the basal heat production, but also shifted the lower critical temperature from 12 to 25C. Attempts to rehabilitate the scaup after oiling and cleaning were rarely successful because of plumage deterioration and the loss of water repellency.