The degree of entrainment is significantly influenced by particle size and density but there is no consensus in the literature, however, on the mechanisms involved. In addition, there has been a lack of rigorous experimental validation of proposed theories. In this study, entrainment tests with only gangue minerals were performed in a 3.5 L laboratory mechanical flotation cell using fully liberated quartz, ilmenite and hematite. The results suggest that the drainage of solids relative to water in the froth (i.e. the degree of entrainment) is a consequence of the balance between the drag force on the particle, and the apparent immersed weight of the particle in the water which potentially changes the particle settling rate. Particle size and density are two variables that affect drag force and apparent immersed weight. Therefore, particles with different particle size and density have different particle settling rates relative to water, and thus exhibit different degrees of entrainment in flotation. A new empirical model for the degree of entrainment was then proposed, incorporating the mechanism underpinning the effect of particle size and density. Results indicate that the model can be employed to predict the degree of entrainment of different gangue minerals on a size-by-size basis. (C) 2016 Elsevier Ltd. All rights. reserved.