The introduction of variable-valency metal compounds into diesel fuel accelerates auto-oxidation by a factor of 1.5-22. Cobalt, copper and chromium compounds are most active, and iron salts least active. A series of mathematical dependences of parameter b, which characterizes the oxidizability of the fuel, on the catalyst concentrations, temperature and the inhibitor (ionol) has been obtained. Ionol weakens the catalytic action of the salts studied on the process of oxidation, reacting with the free radicals arising during the catalytic and non-catalytic decomposition of hydroperoxides of the fuel. The products of oxidation of diesel fuel have been identified from the IR spectrum of the oxidate.