Oil spill over the sea and the river become a serious problem in these days. Two different approaches are used to clean up the spilled oil by means of chemical dispersion and mechanical devices. If it is possible, removing spilled oil using mechanical devices are highly desirable in order not to worry about the secondary contamination from chemical treatment. One of the major unsolved problems using mechanical devices has been the recovery of highly viscous oil spill. So, the systematic experimental data for treating very viscous oil are still wanting. In the present study a series of experiments were carried out to study the effect of the rotational direction of the belt skimmer on the rate of oil recovery using Bunker C oil. Three different situations, namely, upward, downward and up-and-downward pickup rate have been investigated for variable belt speed. The results showed that the rate of oil recovery for downward pickup was much higher than that for upward pickup. The major mechanism to recover the oil using a belt skimmer has been confirmed that oil sticks to the belt surface while moving to the water rather than moving upward. For the removal of spilled oil the optimal belt speed under the present experimental conditions was found to be about 200 ~ 270 mm/s just before the starvation started. The present experimental results would provide the basis for understanding the performance characteristics and physics of various types of skimmers.