An essential oil, is a concentrated, hydrophobic liquid containing volatile aromatic compounds extracted from plants. It may be produced by distillation, expression, or solvent extraction. Essential oils are used in perfumery, aromatherapy, cosmetics, incense, medicine, household cleaning products, and for flavoring food and drink. They are valuable commodities in the fragrance and food industries.

Essential oil is also known as volatile oil and ethereal oil. It may also be referred to as "oil of" the raw plant material from which it was extracted. For example, oil of clove.

Exquisite fragrances and scented bath oils refresh the body and soul.

Prior to the discovery of distillation, essential oils were extracted by pressing, and this is still the case in cultures such as Egypt. Traditional Egyptian practice involves pressing the flower and then burying it in unglazed ceramic vessels in the desert for a period of months to drive out water. The Lotus oil retaining its scent after 3000 years in alabaster vessels in Tutankhamun's tomb was pressed in this manner.

Today, most common essential oils, such as lavender, peppermint, and eucalyptus, are distilled. Raw plant material, consisting of the (flowers, leaves, wood, bark, roots, seeds, or peel, is put in an alembic over water, and the volatile compounds are vaporized. The vapor flows into a cooling tank, and as the steam condenses, the essential oil, which is lighter than water, floats on top. The water is referred to as a hydrosol, or plant water essence. Popular hydrosols are rose water, lavender water, and orange blossom water. Most oils are distilled in a single process. One exception is ylang-ylang, which takes 22 hours to complete distillation. It is fractionally distilled, producing several grades.

Citrus peel oils are usually expressed mechanically, or cold-pressed. These oils are usually by-products of the citrus industry, and thus are much cheaper to produce than distilled oils.

Some flowers contain very little oil, or are too delicate to be distilled, and thus a solvent such as hexane can be used to extract a concrete, or mixture of essential oil and other soluble plant material. The solvent is removed by distillation for re-use. Then alcohol is used to extract the essential oil from the concrete. Since the waxy covering of a jasmine petal is not alcohol soluble, it separates. The alcohol is removed by a second distillation, leaving behind the absolute. Hence, some essential oils such as jasmine and rose are called absolutes.

In supercritical fluid extraction, high pressure carbon dioxide gas is used as a solvent. This avoids the concern of petrochemical residues in the extracted product.

* Basil is used in perfumery for its clear, sweet and mildly spicy aroma. In aromatherapy, it is used for sharpening concentration, its uplifting effect on depression, and to relieve headaches and migraines. Basil is an emmenagogue and should be avoided in pregnancy.
* Bergamot is one of the most popular oils in perfumery. It is an excellent insect repellent and may be helpful for both the urinary tract and for the digestive tract. It is useful for skin conditions linked to stress, such as cold sores and chicken pox, especially when combined with eucalyptus oil. Bergamot is a flavoring agent in Earl Grey tea.
* Black Pepper has a sharp and spicy aroma. Common uses include stimulating the circulation and for muscular aches and pains. Skin application is useful for bruises, since it stimulates the circulation.
* Citronella oil, obtained from a relative of lemongrass, is used as an insect repellant and in perfumery..
* Tea tree, eucalyptus, sandalwood oil, and many other essential oils have topical (external) antimicrobial (i.e. antibacterial, antifungal, antiviral, or antiparasitic) activity and are used as antiseptics and disinfectants.
* Clove oil is a topical analgesic, especially useful in dentistry. It is also used an antiseptic, antispasmodic, carminative, and antiemetic.
* Lavender oil is used as an antiseptic and for a number of other folk medicinal uses.
* Yarrow oil is used to reduce joint inflammation and relieve cold and influenza symptoms.