A recognized challenge in bitumen extraction is the reduced bitumen recovery when processing high-fine ores or "weathered" oil sand ores, collectively called poor processing ores. Preliminary lab tests demonstrated that bitumen flotation recovery from these ores could be greatly enhanced by using oily bubbles (air bubbles coated with a thin layer of oil or solvent) instead of air bubbles. In this study, dynamic contact angle of air/oily bubbles on bitumen surface and induction time of bitumen-air/oily bubble attachment in aqueous solution were measured to investigate the mechanisms of how oily bubbles help improve bitumen recovery and to justify the use of oily bubbles while processing poor oil sand ores. Oily bubbles showed a marginal effect on the contact angle values compared to air bubbles. However, the spreading of oily bubbles on a bitumen surface was found to be much faster than that of air bubbles. The induction time for bubble-bitumen attachment in the process water from poor processing ores was found to be much shorter for oily bubbles than for air bubbles. The reduced induction time for kerosene-coated air bubble-bitumen attachment correlates well with the improved bitumen recovery from poor processing ores using kerosene-coated oily bubble flotation technology. (C) 2005 Elsevier Ltd. All rights reserved.