Viscosity is a measure for the thickness or the thinness of a fluid. High-viscosity fluids are thick and flow sluggishly while low-viscosity fluids are thin and flow freely. High-viscosity oils therefore form thicker lubricant films, providing reliable wear protection for gears and bearings. Low viscosities – especially with engine oil – mean reduced splash losses and hence, improved efficiency and reduced fuel consumption. In manual transmissions, the shift forces increase with increasing viscosity, resulting in reduced operational comfort.