Vapor pressure equations for pure and impure liquid oxygen have been obtained between the normal boiling and freezing points. Comparison of these vapor pressure equations with those obtained by others revealed some numerical disagreement among them. Experiments indicated that a sample may be induced to yield any of a set of vapor pressure values at a given temperature, depending on the experimental circumstances, and therefore great care should be exercised when relating the properties of the used 'pure' samples to those of an ideally pure substance.