Due to its high carbon content, low impurities, low cost and easy availability, poly(ethylene terephthalate) (PET) waste is considered as a suitable precursor for the production of activated carbon. The chemical activation of PET wastes using different chemical agents such as H3PO4, H2SO4, ZnCl2, and KOH was investigated. KOH- and ZnCl2-activated PET were found to be the best choices for the adsorption of small and large molecules. The capacities of the adsorbents towards I2, methylene blue, N2, CH4, and CO2 followed the order KOH-PET>H3PO4-PET>ZnCl2-PET>H2SO4-PET; however, in the molasses uptake and selective adsorption of CO2 compared to CH4, ZnCl2-PET performed better than the other adsorbents.