This study aims to provide distributors with several implications on the channel strategy by testing factors which influence on the offsetting investment. Medium-sized distributor facing a relatively inferior power can cause profit vulnerability from large manufacurer's opportunistic behaviors. At the same time, we tested the relationship commitment to the relation with manufacturer as another alternative strategy taken by medium-sized distributer. For this research, samples from dealers in oil-petroleum refinery industry were selected and the data was collected using mail survey. The data was analyzed utilizing validity test, reliability test, factor analysis, correlation analysis and LISREL. The major analyzed results are as follows: First, the offsetting investment of preventing loss from manufacturer's opportunism didn't affect medium-sized distributor's sales empirically. Second, the hypothesis that the more the medium-sized distributor's transaction specific assets which they invest in the transactional relationship with manufacturer, the more the safeguard against the expected opportunism of manufacturer was not supported by the results. Third, the more use of coercive power by the manufacturer, the more increase in the perception of expected opportunism of manufacturer by the medium-sized distributor, it make stimulates offsetting investment as safeguard by medium-sized distributor and it has negative effect on developing commitment. Finally, the large manufactures dealing with a medium-sized distributor firm which had a reputation of fairness didn't make offsetting investment as a response for distributor's opportunism.