The status of in-situ microbial enhanced oil recovery methods (MEOR) is reviewed. It is shown that the method shows considerable promise as an economical alternative to conventional EOR processes. Several major technical problems, however, still exist in the application of MEOR methods. These include strain selection and improvement, competitive growth and control of in-situ microbial populatons after injection of nutrients, transportability of injected bacteria into the reservoir to minimize permeability impairment and selection of suitable injection strategies. The extensive literature in these areas is reviewed. The need for further research in certain critical areas, as perceived by the authors, is clearly demonstrated. It is evident from this review that a lot more research needs to be done in these areas before the process can gain wide commercial acceptance.