Anaerobic bacteria have been isolated from hydrocarbon reservoirs, varying in depth of burial from 3500ft to 15000ft, at temperatures up to 150°C. These bacteria can be introduced in to the reservoir as a result of drilling operations and/or injection water; however in many cases the bacteria are indigenous to the oilfield reservoir. These bacterial populations have been shown to vary with changes in temperature, affecting their type and bacterial by-products such as pyrite, biopolymer and hydrogen sulphide gas. Using this thermal information, it is possible to construct a model from the incubation of preserved oilfield core samples in various growth media at selected temperatures to determine those areas at high risk of microbial formation damage. This is only a simple first step model as there are many other factors, some only poorly understood, that can affect the growth rate of bacterial populations in a hydrocarbon reservoir such as nutrient availability, sulphide, nitrate, sulphur, hydrogen and phosphate content for example.