To achieve a functioning and stable process with high methane production, it is important to create and maintain a beneficial environment for the activity of bacterial consortia of suitable species. Therefore, an experiment has been carried out to isolate methanogenic and nonmethanogenic bacteria from anaerobic biogas system. With this view, a microbial consortium and their relative performance with respect to individual species in consortia were studies with respect to methane generation. Eight bacterial species have been isolated from the biogas slurry prepared from cow dung. The morphological and microscopic studies have been carried out to study its gram staining properties. The biochemical tests of sugar fermentation, glucose, sucrose, lactose and dextrose shows that the isolate No. 1, 2 and 6 does not respond for this test but the remaining isolates showed positive response. Based on the fluorescence test, isolate 2, 6, 7, 8 are methanogenic and 1, 3, 4, 5 are nonmethanogenic in nature. The methane production of methanogenic and nonmethanogenic bacteria in consortia shows that methanogenic bacteria contribute more rather than nonmethanogenic bacteria. But when the studies were carried out by taking individual species of bacteria, it has been observed that the isolate No. 2 and 4 are most efficient to produce more methane, where isolate 2 is methanogenic and isolate 4 is nonmethanogenic. It shows that the individual species works in better way rather than in consortium in the biogas system. From the above study it was observed that the consortia "C" containing four different methanogenic bacteria are involved in the transformation of complex high molecular weight organic compounds to methane generation (76 %) in comparison to the Consortia "A" (23 %) and Consortia "B" (1%).