The microbial community varied with the time of incubation from the analysis of bacteria and archaea 16S rRNA gene clone libraries. Relative proportion of bacteria lineages (a) and archaea lineages (b) in the four stages during the methanogenic alkanes-degrading enrichment culture. “Stage I” represents the original oily sludge sample from Shanghai Oil Refinery; “Stage II” represents the initial enrichment culture of oily sludge sample without any additional carbon source and incubated for more than 500 days; “Stage III” represents methanogenic enrichment transfer incubation from “Stage II” amended with n-alkanes as the sole carbon source for another 500 days, for details see Wang et al. (2012). “Stage IV” represents the second transfer incubation from “Stage III” for over 1,300 days.