Oil and gas operations worldwide are impacted by the presence of microorganisms. A variety of microorganisms can be found in the oilfield, dependent on the type of operation, geology, location, water source and water treatment utilized. Biocides are used in all stages of oil and gas development to control microorganisms and their detrimental impacts on production such as corrosion, biofouling, and souring. A wide number of biocides are used to control microorganisms, ranging from oxidizing biocides that react quickly but leave no residual activity, to preservatives which act slowly, but provide antimicrobial activity for weeks or months at a time. The spectrum of biocides used in oil and gas are covered by several excellent reviews and will not be detailed in this paper.