The oils of both the bitter and sweet orange-peel are articles of commerce, and prepared in southern Europe by rapturing or grating the ripe fruit, like the lemon, and expressing, or by distillation, 1,000 to 1,500 fruits yielding two pounds of oil. Especially the residue of the expressed peel is sometimes distilled with water, whereby it yields a less fragrant volatile oil.

As all peel-oils suffer in aroma by heat, the best qualities are therefore prepared by expressing. The volatile oils of the two orange peels are distinguished as oil of sweet orange-peel {oleum aurantii dulcis) and oil of bitter orange-peel {oleum aurantii amari). The first is usually employed by carbonators, being somewhat cheaper than the other, and differing from the latter somewhat in flavor, and in being more readily altered by exposure to air; the two oils, however, are alike in chemical composition and in all their essential properties. Oil of orange is of a pale or greenish-yellow color, limpid, varies in its specific gravity between 0.835 and 0.885, boils near 180° C. (356° F.), having a neutral reaction to test paper, an agreeable orange odor, and an aromatic slightly bitter taste. It dissolves freely in absolute alcohol, and requires about two parts of alcohol and about eight or ten parts of alcohol, specific gravity 0.850, for solution; oil of sweet orange-peel dissolves more readily than the bitter variety. Exposed to the air, oil of orange gradually becomes thicker, and acquires a terebinthinate odor. This change is prevented, or at least considerably retarded, by adding to the oil five per cent, of strong alcohol (about one ounce to one pint of oil), and decanting or filtering, if necessary, from the precipitate; as recommended by the Pharmacopoeia. In regard to selection, adulteration and restoration of oil of orange, apply the same rules as to oil of lemon.