The densities of essential oils from traditional herb and New Zealand native species were measured over the temperature range 20°-60°C. The density of all oils decreased as temperatures increased. There was some variation between oils in the temperature coefficients of the change in density. The density differentials between oil and water and their temperature coefficients varied markedly between the different oils. A preliminary separation coefficient is used to indicate the effect of oil density and condensate water viscosity on oil separation at different temperatures. Separation of less dense oils with small differentials (fennel) would benefit more from increased temperatures than less dense oils with large differentials (coriander). It is necessary to use both density and viscosity data to determine if temperature control of a separator will be required to obtain efficient separation of an oil from the condensate stream.