Abstract: This disclosure concerns an improved process for preparing a synthetic hydrocarbon lubricant composition, said composition consisting essentially of di-long-chain alkyl-substituted aromatic hydrocarbons. The improved process is directed to a two-step alkylation process, using linear mono-olefins as the alkylating agent, and in which the first alkylation is conducted using HF as the catalyst, wherein the improvement comprises using aluminum chloride or aluminum bromide as the catalyst for the second alkylation step. Use of aluminum chloride or aluminum bromide, instead of HF, in the second alkylation step results in a product having better low temperature properties.