Bacteria which proliferate in aqueous oil shale waste effluent were studied in an attempt to determine how these waste waters were affected by their growth. Bacteriological analysis of the retort water initially required development of a culture medium for isolation and selection of microorganisms. The medium, retort water agar, incorporated retort water to fulfill carbon and energy requirements of bacteria. It was supplemented with nitrogen and phosphorus and sterilized by a membrane filtration procedure.