There are three methods for extracting vegetable oils from plants. The relevant part of the plant may be placed under pressure to "extract" the oil, giving an expressed oil. Oils may also be extracted from plants by dissolving parts of plants in water or another solvent. The solution may be separated from the plant material and concentrated, giving an extracted or leached oil. The mixture may also be separated by distilling the oil away from the plant material. Oils extracted by this latter method are called essential oils. Essential oils often have different properties and uses than pressed or leached vegetable oils. Macerated oils are made by infusing parts of plants in a base oil a process known as maceration. Although most plants contain some oil, only the oil from certain major oil crops complemented by a few dozen minor oil crops is widely used and traded. These oils are one of several types of plant oils. Vegetable oils can be classified in several ways, for example:
By source: most, but not all vegetable oils are extracted from the fruits or seeds of plants, and the oils may be classified by grouping oils from similar plants, such as "nut oils".
By use: oils from plants are used in cooking, for fuel, for cosmetics, for medical purposes, and for other industrial purposes.
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