Advances in DNA sequencing technologies over the last decade have propelled the ease in which very large data sets on microbial populations can be acquired. The most generally applicable technologies are those that minimize sample manipulation utilize a comparatively unbiased approach toward organism identification and that give statistically significant data on the types and relative abundance of different organisms. We have been utilizing a pyrosequencing-based platform to acquire information on microorganisms in a wide variety of Oil and Gas industrial samples. Hundreds of samples have been analyzed providing the identity and relative abundance of millions of bacteria. Extracting summary information from this large data set is crucial to utilize it in real world applications. We have chosen to categorize microorganisms based on physiological traits of relevance to the O&G. These include sulfidogenesis (hydrogen sulfide generation) acid production iron reduction nitrate reducing sulfur oxidation and the ability to degrade hydrocarbons. Here we present a summary of the relative abundance of each physiological type of bacteria. The origin of these organisms both from exogenous (introduced waters) as well as formation waters can be inferred to some extent from the population structure. Application of this large data set toward developing rational approaches towards microbial monitoring is a primary goal. This data set is being used to calibrate “real time” monitoring technologies and to choose test subjects for treatment efficacy trials.