The state of aggregation in alumina, zirconia, and mixed alumina-zirconia suspensions is determined by particle size analysis of particles/aggregates in suspensions. An aggregation index is derived using principal component analysis of the size distribution data. The first principal component is shown to be an adequate single-value measure of the extent of aggregation in the suspension. Aggregation indices are obtained for suspensions prepared at different pH with and without the addition of different polymeric surfactants of varying dosage and molecular weight and employed for analyzing the state of the suspensions.