Accurate bacteria population monitoring is important in oil and gas fields to mitigate microbiologically influenced corrosion (MIC) prevent reservoir souring and optimize biocide treatment strategies. Serum serial dilution testing (SSDT) is a flawed yet widely accepted traditional method for bacteria testing in the oil and gas industry. The serum bottle test is cumbersome to perform correctly in the best of conditions and impractical to use in most if not all oil and gas field applications. The SSDT culture method returns an indirect estimate of bacteria populations that are often misleading and inaccurate due to basic assumption of the test and users attempts to stream line the method.It is important for operators to understand the drawbacks of the SSDT method and be aware that alternative accurate field ready techniques for bacteria population measurements are available. This paper reports the work performed to a develop a new method to detect bacteria in oil and gas fields that is used to select test and apply fit for purpose bacteria control chemicals.The new methodology has many advantages over other commonly used methods such as the SSDT and ATP tests. The new technique provides a rapid bacteria measurement that can be performed wholly at the well site with real time results. The method gives highly accurate data simple to use and is compatible with oilfield production chemicals fluid chemistries and system microbiology. The approach uses a bacteria metabolism based assay technique that utilizes fluorescence spectroscopy to obtain a fluorescence value that is proportional to the total number of living bacteria present in a sample. However the new method is unique in that the user converts the fluorescence value into meaningful data such as colony forming units per mL or even number of equivalent bug bottle turns. The conversion is based on the results of thousands of experiments comparing the fluorescence value with accurate laboratory bacteria measurements (e.g. plate counts and nucleic acid base testing) performed on field waters from a wide variety of sources.The new technique has been used in many oilfields throughout the world and several case histories are presented where the technique has been used to successfully optimize biocide treatments. This new approach to bacteria monitoring is unique and allows immediate real-time post treatment testing to ensure biocide applications are effective.