The objective of this project is to perform a microbially enhanced oil recovery field test pilot test in the Southeast Vassar Vertz Sand Unit (SEVVSU) in Payne County, Oklahoma. Indigenous, anaerobic, nitrate-reducing bacteria will be stimulated to selectively plug the flow paths which have been preferentially swept by a prior waterflood. This will force future flood water to encounter regions of the reservoir bypassed by the first flood, thereby increasing sweep efficiency. During this quarter studies were made to characterize the in situ bacteria in brine samples recovered from various locations in the SEVVSU. The characteristics of five anaerobic nitrate-using bacteria have been investigated. 2 refs., 4 figs.