In order to assess the effect of biosurfactant (produced by either bacteria or yeast) in experimental microcosms to treat diesel and crude oil pollution, several parametes such as changes of aerobic and hydrocarbon-degrading bacteria, amount of total and hydrocarbon components of petroleum during bioremediation were examined. The results showed that during the biodegrading process in the treated microcosms, the number of hydrocarbon-degrading bacteria was increased and more dominant than that in the control. At the highest hydrocarbon degradation stage, the hydrocarbon-degrading bacteria made of 50-70 percent and 20-45 percent of the total aerobic bacteria in the microcosms supported by bacterial and yeast biosurfactant, respectively. Becides, the decrease in total and hydrocarbon components of the petroleum could also serve as a proof for the effectiveness of biosurfactant products in oil degradation. Thus, approximately 99-100 percent and 41-60 percent of total petroleum
41-75 percent saturate hydrocarbons
29-65 percent aliphatic hydrocarbon
27-43 percent resine and asphaltene in treated and control microcosms were removed, respectively. The data obtained in this study support the application of biosurfactant-producing microorganisms in the treatment of oil pollution along coastlines in Vietnam.