A previously developed model for the heat and mass transfer of a single superheated bubble during the ascension stage was extended to include the formation stage. It allows variable properties and bubble radius changes, solving the gas conservation equations coupled to a bubble dynamics model. Its results were used to predict the existing experimental data in a direct contact evaporator with good agreement. A correction factor for isothermal gas holdup correlations can be fully calculated by the model enabling good prediction of gas hold-up. The constant property assumption overestimates the gas hold-up and should not be used. Experimental data for steam bubbling process could be reasonably simulated using the superheated bubble model with some additional assumptions,