Collectors are important for the effective operation of flotation process. In this work, a new collector was evaluated and compared with diesel oil to investigate its effect on coal flotation. The kinetics of collector spreading on hydrophobic and hydrophilic coal surfaces was studied by measuring the contact angle at coal-oil-water three-phase contact line versus time for the new collector and diesel oil, respectively. The interfacial tensions of each collector with water, as well as their binary mixtures at different compositions, were also studied to elucidate the difference between these two collectors. The performance of the new collector on bench-scale flotation of a hard-to-float coal was compared with that of diesel oil. Both flotation recovery and selectivity were improved with the adoption of the new collector. Comparing with diesel oil, the better flotation results obtained using the new collector can be attributed to the lower interfacial tension of the latter, resulting in faster collector spreading on coal particle surface and possible smaller collector droplet size formed by dispersion in a mechanical stirring cell. The size assay of the flotation concentrates indicated that the flotation recovery of medium-to-coarse coal particles (38-600 mu m) increased as the collector interfacial tension decreased. However, there may be an optimal value of collector interfacial tension, corresponding to the maximum flotation recovery for ultratine coals of -38 mu m.