Numerical simulation of bubble formation process from a stagnant nozzle immersed in a quiescent liquid (water) and from a nozzle located on a rotating cylinder set in a cross-flowing liquid was performed with the aid of a computational fluid dynamics (CFD) code. Solution of momentum balance equations was coupled with VOF algorithm for tracking the gas-liquid interface in 2D and 3D domains. The results of the simulation are compared with the experimental data obtained from a high-speed video camera observation. The agreement was favourable in the case of rotating nozzle. In the case of a stationary nozzle, the VOF algorithm seems to perform best when the process is dominated by inertial forces (higher gas flow rates).