Whilst molecular tools have been employed for a number of years within the oil and gas industry the results have largely been of academic interest and of limited additional value to solving problems.More recent advances in techniques are providing scope for evaluation of potential microbially influenced problems in a variety of situations; however there still remain challenges with interpretation of the data being generated. In many cases molecular biology enables one to confirm the presence of groups of microorganisms that may be implicated in corrosion or hydrogen sulphide generation. None the less there remains considerable work to be undertaken to define criteria for whether the corrosion events can be attributed solely to microbial activity.The paper will present case histories from water injection and oil production wells plus a multiphase flowline review results obtained and discuss the degree to which the use of molecular monitoring has helped to more fully explain the observed events.