This paper gives a description of a computer simulation model called North Atlantic Simulation and Modelling developed by Virginia Tech’s Air Transportation Systems Laboratory. The model is capable of investigating the effects of implementing different operational policies and strategies in oceanic airspace such as Reduced Lateral Separation Minima, North Atlantic Region Data link mandate, Reduced Longitudinal Separation Minima, cruise-climb profiles, variable Mach number profiles, step-climbs and other operational concepts. This paper describes the methodology, various components of the model and validation results. The effects on aircraft fuel consumption due of ICAO's North Atlantic data link mandate and reduced lateral separation minima, which are being implemented in the North Atlantic airspace are also discussed.