Expeller pressing methods have a long history of extracting vegetable oil from oil seeds; the methods involve some means of mechanically squeezing oil from crushed oil-containing seeds under an applied pressure. Most cooking oils are produced via expeller pressing of a variety of feedstock including maize, sunflower, soya, sesame, coconut, mustard seed, and groundnuts. Even though this mechanical extraction method of oil from oil seeds is tech­nologically very simple, the process has been significantly enhanced with the development of energy-efficient and mechanically superior machinery. Furthermore, large processing plants have advantages over small plants in terms of reduced processing cost and extraction efficiency; most countries have such centralized large plants for cooking oil manufacture. These plants are also known as "oil refineries," that is, vegetable oil refineries. However, logistical burdens and transportation costs of raw materials and finished products also make small-scale highly efficient plants relevant and viable options. This is especially true for algae oil and biodiesel processing.

Oil presses are typically used for vegetable oils and biodiesel process­ing on both large and small scales. There are two different kinds of large — scale processing methods involving oil presses, one being hot processing
and the other being cold processing. In hot processing, the system includes a steam cooker and oil press. The steam cooker is mainly for pretreatment of oil seeds. In cold processing, the machine operates at a low temperature (e. g., 80°C) when it presses the seeds. An advantage of cold processing is that the extraction environment is not destructive to the nutrients in the oil. Dry algae can also be processed, quite similarly to oil seeds, using an oil press for extraction of algae oil, by mechanically rupturing the cell walls and collect­ing the extracted oil.