Abstract:The effects of operation practice on board ships on microbial growth in marine fuel was examined. With temperatures above 65°C, no microbe was observed after 3-days of incubation and the total counts of Pseudomonas maltophilia and Escherichia coli decreased with time. The viability of reference strains in oil samples with four different water contents under four temperatures was also determined. Under 25°C, the total number of viable fungi with 20% distilled water and 10% seawater drop to zero within 10 days. No viable fungi were observed in oil samples with 0 or 5% water after 2-days incubation. Fungi recovered to significant degree thereafter, in all samples containing water.