In wet milling, the presence of a pool of slurry is generally the result of mill overfill. The effects of overfilling on milling kinetics have been examined. Assessment of milling efficiency has also been made. To this end, batch grinding tests were carried out at 75% of critical speed. A laboratory mill, filled with 20 mm balls, was used for the tests. Two levels of ball volumetric filling were considered: J = 20 and 30%. Slurry filling U was varied from 1.5 to 3.0 with reference to 20% ball filling. Equal masses of slurry were also used for a 30% ball filling which made slurry filling U change accordingly. Net power draw was measured throughout the experimentation. It was found that product size distribution is a definite function of slurry filling U. Graphical analysis of the results suggests that the voids within the media charge should be completely filled with slurry without allowing the formation of the pool. This way, optimal output shall be expected. Moreover, mill power drop due to slurry pooling did not result in a proportional decrease in the production of fines. (C) 2014 Elsevier By. All rights reserved.