Aerobic heterotrophic bacteria were enriched and isolated from three oil storage caverns of the German national oil reserve at different distances from the oil/brine interface. Microscopically no bacteria were found in the original samples, but colony counts showed more than 100 colony-forming units (cfu)/ml in two samples, whereas 0 to 4 cfu/ml were found in the other samples. Enrichments using defined mineral salts medium or complex medium revealed culturable organisms in all samples. All colony types were isolated and further separation of organisms during isolation was completed microscopically. Enrichments in media containing complex organic compounds led to higher numbers of isolates in samples near the oil/brine interface than enrichments with oil as the sole source of carbon. Micro-organisms that could utilize oil as the sole source of carbon were isolated from all enrichment cultures. Identification of the isolates revealed Bacillus strains in all samples and coryneform bacteria in the samples from cavern 123.