Extra high performance 40 TBN oils designed for use in the most severe residual-fuelled, medium speed diesel engines in marine and stationary power applications. These diesel oils have been specially formulated to provide outstanding residual fuel compatibility characteristics for excellent engine cleanliness, especially in crankcase, camshaft areas, ring belt and piston undercrowns. They provide excellent high temperature oxidation and thermal stability, low volatility, and high load carrying properties and corrosion protection.