Sustainable lubricant compositions made from recycled thermoplastic polyesters and other reclaimed or biorenewable reactants and a method of formulating them are disclosed. The lubricant compositions comprise a polyester base oil, which incorporates recurring units from a digested thermoplastic polyester, a low-molecular-weight polyol, and C8-C24 fatty acid. The base oil has a number-average molecular weight within the range of 300 to 5000 g/mol, a hydroxyl value less than 50 mg KOH/g, and a viscosity at 40° C. less than 5000 cSt. Some of the lubricant compositions comprise the polyester base oil and one or more additives including anti-wear agents, corrosion inhibitors, antioxidants, thickeners, detergents, and the like. The lubricants have properties that rival those of commercial products made from nonrenewable hydrocarbon blends or polyol esters and are useful for many practical applications such as internal combustion engine oils, gear lubrication oils, hydraulic oils, compressor oils, metal working flu
