Abstract In order to explain the origin of the Lake Nyos Disaster, a three-dimensional model for carbon dioxide flow has been calculated. The boundary conditions were based on the field observations. Calculations show that CO 2 tends to flow down slope by gravity and velocity tends to increase on steep slopes. The results of calculation are in good agreements with the effects observed in the field. The initial velocity of the gas jet should have been 28 m/s, the volume of pure CO 2 0.6 km 3 and the gas release should occur in a very short time (a few minutes). The gas was released as a jet half way from the center on the south-south west side of the lake.