This paper presents a theoretical model and experimental results of the generation of bubbles due to the injection of a constant flow rate of gas through an orifice submerged in liquid. The bubble formation process can be identified into three distinct stages termed (1) nucleation stage, (2) growth stage, and (3) detachment stage by analyzing the evolution of interface equilibrium and force balance conditions. Influence of contact angle on bubble formation at each stage is quantitatively elucidated. Experimental investigations in the preparation process of aluminum foams by gas injection method were conducted, and the generated bubble size was measured. The theoretical prediction of the present model suits well with the experimental results when a contact angle of 30A degrees is introduced. The present model covers a wide range of contact angle (theta < 90A degrees) at different gas flow rates and orifice radii in both aqueous and metallic systems.