NOVELTY - The method comprises introducing a performance-enhancing denaturant component to a biofuel comprising ethanol to form a fuel mixture for fueling the internal combustion engine, and introducing a hydrocarbon-based fuel to the fuel mixture. A portion of the performance-enhancing denaturant component combines with an engine lubricant oil in the engine during operation to improve engine performance for increasing fuel economy in comparison to the engine fueled by a comparative fuel lacking the performance-enhancing denaturant component.    USE - The method is useful for increasing fuel economy of an internal combustion engine consuming a biofuel.    ADVANTAGE - The method provides continuous introduction and/or replenishing of active additive components to the lubricant engine oil delivered through the fuel thus achieving the good increase of fuel economy of greater than or equal to 5%, lubrication and/or durability of the engine, and reduces the degradation of engine lubricant oil thus enhancing the engine performance and engine oil life.    DETAILED DESCRIPTION - The method comprises introducing a performance-enhancing denaturant component to a biofuel comprising ethanol to form a fuel mixture for fueling the internal combustion engine, and introducing a hydrocarbon-based fuel to the fuel mixture. A portion of the performance-enhancing denaturant component combines with an engine lubricant oil in the engine during operation to improve engine performance for increasing fuel economy in comparison to the engine fueled by a comparative fuel lacking the performance-enhancing denaturant component. The performance-enhancing denaturant component comprises an organic ingredient consisting of friction modifiers, lubricity enhancers and/or anti-oxidants, and an additional ingredient consisting of surface-active agents, detergents, co-solvents and/or compatibilizing agents. A final biofuel composition comprises the ethanol. The performance-enhancing denaturant component has an end boiling point of less than 225 degrees C. INDEPENDENT CLAIMS are included for:    (1) a biofuel composition; and    (2) a method for formulating a biofuel for use in an internal combustion engine.