Synthetic lubricating oils having a predetermined alkylaromatic structure are prepared from a mixture of mono- or dialkenyl benzene with an aliphatic olefin by free-radical reaction in the presence of ditertiary-butyl peroxide, for example. Equivalent napthalene derivatives may be substituted for the dialkenyl benzene. The oils that are formed exhibit a high Viscosity Index, and a low pour point. The viscosity of the synthetic lube stock produced may be controlled by changing the amount of peroxide used.