Display omitted •Simultaneous degradation of phenolic compounds in AnMBR under saline conditions.•Increased concentration of the phenolics decreased their uptake rates in batch test.•Stronger methanogenic inhibitory effects with p-cresol than resorcinol.•Thermodynamic analysis explaining syntrophic associations in the AnMBRs.•Phylogenetic similarity of p-cresol- and resorcinol-degrading microbial communities. Treating petrochemical wastewater is a challenge for conventional anaerobic reactors. One example is coal gasification wastewater that, besides its salinity, is rich in toxic and inhibitory aromatics, such as phenol, cresols, and resorcinol. Studies have shown that phenol and p-cresol share the same degradation intermediates, whereas resorcinol is degraded via another route. This study investigated the simultaneous degradation of p-cresol or resorcinol with phenol under anaerobic saline conditions. Batch experiments with anaerobic phenol-degrading biomass were conducted to assess the feasibility of the degradation of p-cresol and resorcinol. Volumetric uptake rates of 11.4 ± 2.4 mgp-cresol·L–1d–1 and 4.2 ± 1.9 mgresorcinol·L–1d–1 were determined. The effect of p-cresol and resorcinol on the specific methanogenic activity and the cell viability in phenol-degrading and non-adapted biomass was assessed. Half maximal inhibitory concentration (IC50) values of 0.73 gp-cresol·L-1 and 3.00 gresorcinol·L-1 were estimated for phenol-degrading biomass, whereas IC50 values of 0.60 gp-cresol·L-1 and 0.25 gresorcinol·L-1 were estimated for the non-adapted biomass. p-Cresol caused a higher decrease in the non-damaged cell counts in comparison to resorcinol. Two anaerobic membrane bioreactors under saline conditions 8 g Na+·L–1 were fed with mixtures of either phenol-p-cresol or phenol-resorcinol. At an influent phenol concentration of 2 g·L-1, maximum conversion rates of 22 mgp-cresol·gVSS-1d–1 and 16 mgresorcinol·gVSS–1d–1 were found. In both AnMBRs, Syntrophorhabdus sp. and Methanosaeta sp. were the most abundant bacteria and methanogen, respectively. The feasibility of simultaneous conversion of phenolic compounds under saline conditions in AnMBRs opens novel perspectives for the high-rate anaerobic treatment of chemical wastewater.