The principles underlying the evaporation of moisture from oil bearing materials are discussed with especial reference to rapid testing. Two forms of rapid moisture testing apparatus employing relatively high temperatures and strong induced draft, are described. Data are given to show how the results compare with determinations made in a conventional oven at the usual drying temperature, as well as a tabulation comparing the results obtained by an untrained plant operator using the rapid tester with checks on the same samples made in the laboratory. The advantages inherent in rapid moisture testing from the control standpoint are discussed. Finally, the application of the apparatus as a controlled-heat hotplate is suggested.