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Two indigenous bacterial consortia, IMP-100 and IMP-200, proved to have a functional effect on heavy crude oil recovery, indicating a potential implementation in Microbial Enhanced Oil Recovery (MEOR). Growth kinetics of the indigenous bacterial population was performed under anaerobic conditions at 70 °C and 33 g L −1 of salinity. It was found that both extremophile consortia were able to grow under the latter conditions. Moreover, they synthesized metabolites that altered the surface properties of the supernatants derived from cell cultures, a useful property in oil recovery processes. Ex situ fermentations in the presence of crude oil-impregnated calcite rocks demonstrated that both bacterial consortia enhance crude oil recovery by 8.5% and 13%. In order to identify possible phenomena responsible for incremental oil recovery, emulsification index ( E 24 ), surface tension, cell adhesion to hydrocarbons, and crude oil viscosity were characterized. The results demonstrate that IMP-(100, 200) consortia were able to recover heavy crude oil from calcite rocks, possibly due to a decrease in crude oil viscosity, induced by the presence of metabolites and/or the interaction between bacteria and oil hydrocarbons. [ABSTRACT FROM AUTHOR]