A large number of studies were carried out in the past to analyze the significance of colloids and microbes in remediating groundwater aquifers contaminated with petroleum hydrocarbons. However, the influence of the co-occurrence of colloid and microbe on the migration of petroleum hydrocarbons is still poorly understood. In the present study, an attempt is made to numerically investigate the impact of the co-occurrence of colloids and microbes on the transport of BTEX (benzene, toluene, ethylbenzene, and xylene). A finite-difference model is developed to analyze the co-transport of colloid, microbe, and BTEX within a saturated porous aquifer. The present model is formulated based on the assumption that the colloid migration within the aquifer is not affected by the presence of microbe and BTEX. The microbe presented in the manuscript is deemed to biodegrade the BTEX constituents aerobically. Hence, the modeling study also incorporates the migration of dissolved oxygen within the aquifer. The results obtained from the simulation study suggest that the co-occurrence of colloid and microbe causes significant retardation in the movement of dissolved BTEX constituents within the aquifer. It is also seen that the presence of colloid considerably enhances the biodegradation rate of BTEX within the aquifer. A sensitivity analysis is carried out to investigate the sensitivity of the concentration distribution of colloid, microbe, and BTEX to various flow and sorption parameters. The concentration level of colloid, microbe, and BTEX constituents is found to be sensitive to the variation in the flow and sorption parameters.