The impact of polydimethylsiloxane (PDMS) on oxidation of soybean oil at frying temperatures was investigated. At concentrations of PDMS greater than that calculated to be necessary for a compact monolayer on the oil surface, the rates of degradation of linoleate (18:2) and gamma- and delta-tocopherols were slower than in untreated oil. Degradation rates of 18:2 increased after a certain time at frying temperatures, likely caused by a reduction of the tocopherols and/or the PDMS to levels at which they were no longer protective. PDMS decreased oxygen transfer to the oil at temperatures close to frying temperatures. The concentration of 4-hydroxynonenal (HNE), a toxic product of 18:2 oxidation, was affected by PDMS concentration. In general, PDMS retarded HNE formation when used at concentrations greater than the monolayer concentration. PDMS concentrations capable of forming multilayers were more effective than a monolayer, and the protective effect lasted for a longer time. The results strongly suggest that PDMS decreases the oxygen transfer rate into the oil, thus decreasing the degradation of 18:2, tocopherols, and the formation of oxidation products, such as HNE.