Gas pores appear during solidification when the gas concentration in the liquid is higher than the gas solubility at a certain location. In this study, an analysis has been carried out to predict the gas concentration in the melt for different forms of the solidification rate. An exact solution is found for a constant interface velocity. An integral analysis is used to predict the gas concentration behavior for different interface velocity functions, including the most common cases of casting. The maximum gas concentration occurs at the solid-liquid interface and it depends on the form of the solidification rate as a function of time. The results can be used to establish criteria for the maximum amount of dissolved gas permissible in the melt in order to avoid the formation of gas bubbles.