Essential oils can be produced from various plant sources, as well as from different plant parts including resins (plant exudates), leaves, flowers, fruits, bark and wood. Most essential oils are extracted using steam distillation. Other extraction methods include water distillation, expression – most notably from citrus peels (mechanically or cold pressed) – solvent extraction or enfleurage (from flowers). Extraction methods mainly depend on the raw material that is being extracted.