A lubricant composition, method for reducing a boundary friction coefficient of a lubricant composition, and method for improving fuel economy. The lubricant composition includes a base oil, a) a metal-containing phosphorus antiwear compound in an amount sufficient to provide from about 100 to about 1000 ppm by weight phosphorus based on a total weight of the lubricant composition, and b) an oxygen-polymerized vegetable oil, different from the base oil. The base oil is present in the lubricant composition in an amount from about 50 wt. % to about 99 wt. % based on the total weight of the lubricant composition.