A selection of polyolefins and other paraffins has been studied with respect to the mechanism of their decomposition by wet oxidation in a batch autoclave reactor. The general conditions were 2.0 MPa Of 02 at 260-degrees-C. Virtually all hydrocarbons were decomposed into water-soluble compounds and CO2. An analysis of the products indicates that the decomposition proceeds mainly by fragmentation of one or two C-atoms at a time. The yield of the different products was dependent, to some extent, on the type of starting material. A reaction mechanism has been proposed to explain the intriguing occurrence of significant amounts of hydrogen in the gas phase.