Single celled organisms that take the shape of spheres, rods, and spirals. Bacteria grow rapidly under the right conditions and they are found in different habitats. Bacteria play a role in the formation of hydrocarbons and the in-situ alteration/transformation processes such as biodegradation. Bacterial by-products are accumulated and preserved within the sediment and thus can increase the organic content and inherent petroleum source potential. This is because some petroleum molecules such as lipids are found in bacterial cell membranes. Bacteria can also cause the decay of deposited organic material by attacking hydrocarbon molecules in the absence or presence of oxygen.