This chapter describes the history, development, and current use of spray oils that have their origins from animal, vegetable, and petroleum sources. Vegetable and mineral oils have lengthy traditions of use as pesticides; however, recorded use of petroleum oils goes back several centuries. Mineral oils for use on ornamental plants should be labeled as paraffinic. The hydrofining process makes it possible to use crude oils with less paraffins and at the same time control the molecular weight. Pure oil, even the narrow-range variety, is toxic to temperate-zone plants by shutting off the transpiration and respiratory system, both in foliage and bark. Comparisons can be made with biological and synthetic organic insecticides, and in this kind of analysis we can show distinct environmental advantages for the use of oils. Oils have also been used successful, particularly in Utah and the Northwest, for early-season frost protection.