Microbiologically influenced corrosion is a problem commonly encountered in facilities in the oil and gas industries. The present study described fungal enumeration and identification in biofilms of oil pipelines in Oshie flow station in Rivers State and Irri flow station in Delta State, Nigeria using traditional cultivation technique. The fungal species isolated in biofilms from the two sites are as follows Verticillium dahlae, Saccharomyces cerevisiae, Penicillium corylophilum, Botrytis cinerea, Fusarium oxysporum, Aspergillus paradoxus, Humicola grisae, Aureobasidium pullulans, Monilia balanitis, Hormoconis resinea, Asperillus flavus and Helimenthosporium maydis. The study also focuses on the use of three biocides to inhibit or eliminate the identified organisms in order to minimize the material and financial losses encountered by oil and gas companies, because of microbiologically influenced corrosion (MIC). The performance of three biocides (ozone, sodium hypochlorite and formaldehyde) at the concentrations of 0, 1, 2, 3, 4 and 5% in eliminating the fungal species isolated from biofilms of oil pipelines in Rivers and Delta States, Niger Delta, Nigeria. It is shown, that formaldehyde, ozone exhibited the best biocidal characteristics and concentrations of 1 and 2 % eliminated almost all the fungal species after 72 hours of contact time. This study is relevant to the problem of microbiologically influenced corrosion as the data may contribute to elucidate which fungal species contribute to the MIC process and to gain a better understanding of the fungal community of biofilms. This study will give us better understanding of the biocide capable of eliminating fungal species in biofilm of oil and gas pipelines. Keywords: Concentration, fungal population, biocides, microbiologically influenced corrosion, biofilm
