The study of Biodeterioration of Premium Motor Spirit and Automotive Gas Oil by bacterial and fungal deteriogens was conducted to ascertain the level of spoilage on petroleum samples obtained from African Petroleum and Oando Filling Stations, Port Harcourt. The Spread plate technique was employed for the enumeration of the microorganisms. The samples were cultured on petri-dishes containing nutrient media and potato dextrose agar and were incubated at temperature of 28–31°C for 48 hours and 72 hours for bacterial and fungal growth respectively. The bacterial and fungal isolates were further tested for hydrocarbon utilization potential with a modified mineral salt agar at room temperature for 48 hours and 168 hours respectively. Results showed a high range of total viable counts of Bacterial and Fungal species in samples collected from the stations. Bacillus spp., Pseudomonas spp., Aspergillus spp., Penicillium spp. were isolated from Diesel samples; while Pseudomonas spp., Bacillus spp., yeast spp. and Aspergillus spp. were isolated from Petrol. The Petrol and Diesel distributed by the African Petroleum to customers is of a higher quality than that of Oando Filling Station. There was abundance of microbial growth at Diesel substrates and was least supported by Petrol. This may be as a result of heavy contamination of the samples when in the storage tanks underground. The lead, anti-knock additive (tetra-ethyl lead) in Petrol may be the cause of growth inhibition. It is therefore recommended that adequate control-spoilage measures should be taken in order to prevent bioattack of the petroleum products.