Abstract: A method for transitioning between a first engine operating mode and a second engine operating mode of an internal combustion engine involves establishing an engine mode transition region between the first engine operating mode and the second engine operating mode, which engine mode transition region is defined by at least one engine operating parameter. The engine operating parameter which defines the engine mode transition region is monitored. When the engine is operating in the transition region a first engine operating mode fuel rate is determined, a second engine operating mode fuel rate is determined, and an engine mode transition region fuel rate is determined which is a function of both the first engine operating mode fuel rate and the second engine operating mode fuel rate.