<div class="htmlview paragraph">T<span class="small-caps">HE</span> autoignition characteristics of several fuels under various conditions of mixture strength, compression ratio, and temperature have been studied by means of a rapid-compression machine.</div> <div class="htmlview paragraph">The behaviors of a knock inhibitor, tetraethyl lead, and a knock inducer, ethyl nitrite, have also been studied.</div> <div class="htmlview paragraph">Simultaneous records of pressure, volume, and the inflammation have been obtained.</div> <div class="htmlview paragraph">These records show the diverse aspects of the autoignition phenomenon and indicate, among other things, according to the authors, that a comparison of the detonating tendencies of fuels must include not only a consideration of the length of the delay period but also an evaluation of the rate of pressure rise during autoignition.</div> <div class="htmlview paragraph">Physical interpretations of the data are presented but chemical interpretations have been avoided. The work was exploratory in nature. The authors hope that the results will stimulate activity in this important branch of combustion research.</div>