The Citgo CitGard SynDurance Plus Synthetic Heavy Duty Engine Oils' fuel efficiency formula is designed to deliver fuel economy, extreme cold temperature performance and engine durability. These engine oils contain a balance of synthetic base oil components with a shear stable viscosity modifier, which insures heavily loaded engine parts have protective oil films. Citgo CitGard SynDurance Plus Synthetic Heavy Duty Engine Oils meet the performance requirements of newer engines operating at higher temperatures, with lower rpm, higher torque and advanced combustion design.