A discussion of the tests by which the character of petroleum oil may be designated, with special reference to volatility and suffocation in evaluating oils to be used for sprays. The effect of petroleum oils of various specifications on insects and plants. The relative value of different types of oil emulsions as insecticides. Special attention is given to a discussion of the so-called “quick breaking” type of emulsion which was devised for use with very highly refined lubricating oils which are too expensive for general use unless their efficiency as insecticides is increased beyond that found in stable emulsions made from this type of oil. This system of emulsification is recommended only for oils that are practically harmless to the plant if applied pure. The use of very small amounts of emulsifiers permits the oil to separate quickly from the emulsion stage, thus making the oil more effective and decreases the amount of oil in the runoff.