The Department of Defense is a major consumer of petroleum products – over 700 million gallons per day. While the majority of fuel consumed is for aircraft, in terms of logistics and exposure of personnel to hazardous conditions, the amount of fuel consumed in ground vehicles is considerable, with the cost (in-theatre, delivered) ranging from $100 to $600/gallon. This paper addresses the impact that parasitic friction mechanisms (boundary lubrication and lubricant viscosity) have on engine friction and overall vehicle efficiency. A series of mechanistic models of friction losses in key engine components was applied to investigate the impact of low-friction technologies on the fuel consumption of heavy-duty, on-road vehicles. The results indicate that fuel savings in the range of 3 to 5% are feasible by reducing boundary friction and utilizing low-viscosity engine lubricants. The paper will discuss the implications of the studies (as performed for commercial heavy-duty trucks) for military ground vehicles, which have significantly different driving modes. The paper will also discuss the potential of different strategies to implement low-friction/low-viscosity solutions and the impact of these strategies on reliability and durability.