In order to simulate the performance of chemical looping combustion (CLC) of pure methane in a continuous bubbling fluidized bed process using a NiO-based oxygen carrier under various operating conditions, this study has developed a mathematical model based on the reaction kinetics and population balance of oxygen carrier (OC) particles in each reactor. Proper operating conditions have been discussed for complete combustion of methane. The minimum OC circulation rate for complete combustion was determined with the variation of temperature and fuel bed mass. The methane combustion efficiency was strongly affected by the distribution of OC between the air reactor (AR) and fuel reactor (FR) at a constant temperature, circulation rate of OC, and total bed mass. The range of OC distribution possible to achieve complete combustion became wider with increasing either the temperature or the circulation rate of OC at a constant total bed mass. In tested conditions of a lab-scale process, the range on the OC mass ratio of the fuel reactor to the total bed mass extended from 0.527-0.607 to 0.430-0.705 with an increasing temperature of AR and FR from 850 to 900 degrees C (circulation rate of OC = 3 g/s, total bed mass = 22.89 kg). It also extended from 0.527-0.607 to 0.491-0.643 with increasing the circulation rate of OC from 3 g/s to 10 g/s (temperature of AR and FR = 850 degrees C, total bed mass = 22.89 kg). In this range, the amount of elutriated OC particles decreased a little as the FR mass increased because of the higher rates of particle elutriation and attrition in AR than in FR.