Skip to main content

Oil Red O

Oil Red O

Class: Azo
Ionisation: Lysochrome

Chemical structure of Oil Red O

Common Name: Oil red O
Suggested Name: Oil red O
Other Names:

C.I. Number: 26125
C.I. Name: Solvent red 27
Color: Red
Solubility Aqueous: Insoluble
Solubility Ethanol: Insoluble
Absorption Maximum: 518 (359)
Empirical Formula: C26H24N4O
Formula Weight: 408.51


Oil red O is a lysochrome (fat soluble dye) predominantly used for demonstrating triglycerides in frozen sections, but may also stain some protein bound lipids in paraffin sections. It has largely replaced sudan III and sudan IV as it is much deeper red in colour, and consequently more clearly visible.

Compare this dye to the other common lysochromes sudan III, sudan IV, and sudan black B.


  1. R. D. Lillie.
    Conn’s Biological Stains
    Williams & Wilkins, Baltimore, MD., U.S.A.
  2. Aldrich chemical catalogue, 1992
    Aldrich Chemical Company, Milwaukee, WI, USA.