An Othmer type vapour-liquid equilibrium still was used to determine the effect of selected solvents on the relative volatility of 1-octene relative to 2-hexanone. Solvents such as dimethylacetamide, dimethylformamide and methoxyethanol which are highly polar had the greatest effect. An assessment of the dependence of the relative volatility on the molecular properties of thirty-one solvents investigated was also undertaken. Properties such as the dielectric constant (epsilon), dipole moment (mu), polar solubility parameter (tau), solubility parameter (delta), and the polar part of the solubility parameter (delta(p)), which are all characteristic of polarity, have been shown to correlate with experimental relative volatilities.