Reoxidation of liquid steel during transfer from ladle to tundish affects the inclusion characteristics and is harmful to process stability, mechanical properties, and the overall quality of the cast product. A thermodynamic model was developed and a laboratory vacuum induction furnace was employed to simulate the reoxidation of aluminum killed calcium treated steels. Samples were collected at different times and analyzed via automated SEM/EDS. A method for representing the size distribution of inclusions using the population density function (PDF), was applied to study the effect of reoxidation on the inclusion characteristics. The results show that spinel inclusions can be produced after reoxidation if there is sufficient magnesium in solution. A comparison of the size distributions of spinel inclusion populations showed that spinel inclusions produced after reoxidation are larger than those formed prior to reoxidation and calcium treatment.