A one-dimensional model based on mass and momentum conservations has been developed to predict the heights of foams caused by gas injection. In the development of the model, a dimensionless number, N-foam = u(s)[(3C(d))/(4d(b)g)](1/2) has been deduced to characterise the foaming behaviour. According to the model, an increase in this dimensionless number results in an increase In foaming height. The validity of the model has been experimentally examined using silicon oils. The experiments have also shown that foamings can be classified into two types, namely one-layer foaming and two-layer foaming. The former type results in much larger height than the latter.