The effects of supersaturation and steel composition on the morphology of Al2O3 inclusions were investigated. Thermodynamic calculations with Factsage 7.0® were used to predict the degree of supersaturation and select the starting aluminum and oxygen amounts for the experiment. Deoxidation experiments were performed by melting the charge material and using specially designed samplers to study the local deoxidation reactions. The inclusions in the collected steel samples were analyzed on filter paper in 3D after extraction from the steel. The observed Al2O3 morphologies consisted of dendrites and clusters and results showed that increasing supersaturation had the strongest influence on the length of the dendrite. The observed clusters resulted from collision, heterogeneous nucleation and growth on existing Al2O3 inclusions, and possibly oxygen gradients and liquid steel convection during nucleation and growth of Al2O3.