Dual-fuel diesel engine with cylinder fueling control of gaseous fueling at less than full loads

A method, used with dual-fuel engine, of controlling the amount of gaseous fuel delivered to the engine. At operating conditions that result in an equivalence ratio below a predetermined threshold (which typically occur at mid or part loads), it is determined whether better performance and/or lower emissions can be achieved by reducing gaseous fuel to some cylinders and increasing gaseous fuel to others. Typically, the gaseous fuel is reduced to zero to a number of cylinders and increased to others, with the increase resulting in an equivalence ratio that will provide improved emissions and efficiency and the desired engine output.