This paper presents a systematic numerical investigation of airflow during compression in a simplified tablet press geometry. Air entrainment during tablet compression has been cited as the cause of manufacturing defects and quality problems. The effects of tablet punch profile, speed and punch to die wall clearance on airflow in the system are investigated. Conditions under which air entrainment in the tablet formulation are likely to occur have been identified, and are found to correspond with punch concavity. For a flat profile punch, the effects of punch speed and punch to die wall clearance are shown to be of minor importance. (c) 2006 Elsevier Ltd. All rights reserved.