Flotation performance depends on bubble-particle attachment which is controlled by the particle surface properties which include the particle composition and the surface liberation of valuable minerals. This paper discusses the contribution of liberation of valuable minerals to bubble-particle attachment time measurements, under constant chemical conditions. The bubble-particle attachment time measurements were performed using a sized fraction from concentrates obtained at different times and tails by flotation of a copper-gold sulphide ore (Northparkes Mine, Australia) in a mechanically agitated batch flotation cell. All products and tails were analyzed using quantitative mineral liberation analysis. The results showed that there was a relationship between the time of the concentrate collected, the Cu grade of the sample and the bubble-particle attachment time, and that the measurements were most sensitive to the amount of unliberated material. The fast floating material was higher grade, with a lower attachment time indicating that the measured bubble-particle attachment time could be used to characterize flotation performance of an ore. (C) 2011 Published by Elsevier Ltd.