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Geomicrobial prospecting for hydrocarbons is an exploration method based on the seepage of lighter hydrocarbons from oil/gas reservoirs to the surface and their utilization by hydrocarbon oxidizing bacteria. These bacteria utilize the hydrocarbons as their sole source of food and are found to be enriched in the near surface soils/sediments above the oil and gas reservoirs. The detection of anomalous populations of hydrocarbon utilizing bacteria in the surface soils can help to evaluate the prospects for hydrocarbon exploration. Geomicrobial prospecting studies have been carried out to test the efficacy of surface geochemical methods as regional evaluation tools in the petroliferous region of Mehsana Block, North Cambay Basin, Gujarat and to investigate whether the geomicrobial anomalies can establish an upward migration of hydrocarbons from the deep subsurface. In the present study, bacterial counts for n-pentane utilizing bacteria range between 1.0×10 and 9.80×10 cfu/g and and n-hexane utilizing bacteria range between 1.0×10 and 9.20×10 cfu/g. The bacterial concentration distribution maps show four distinct anomalies in the study area. The possibility of discovering oil or gas reservoirs using the microbiological method is emphasized by the fact that the hydrocarbon oxidizing bacteria range between 10 and 10 cfu/g in soil/sediment receiving hydrocarbon microseepages. In the present study area of the Mehsana Block of Cambay Basin, n-pentane and n-hexane utilizing bacteria show 10 cfu/g of soil sample, which is significant and thereby substantiates the seepage of lighter hydrocarbons from oil and gas reservoirs. Geomicrobial prospecting method has shown good correlation with existing oil/ gas fields of Mehsana, Gujarat. [ABSTRACT FROM AUTHOR]