Four different vegetable oils, degummed soybean, once refined cottonseed, peanut and sunflower oils, were injected into a high-pressure, high-temperature environment of nitrogen. The environment was controlled to resemble, thermodynamically, conditions present in a diesel engine at the time of fuel injection. Samples were removed from the sprays of these oils while they were being injected. A sonic, water-cooled probe and a cold trap were used to collect the samples.Chemical analyses of the samples indicated that significant chemical changes occur in the oils during the injection process. The major change is the formation of low-molecular weight compounds from the C18:2 and C18:3 fatty acids.