Highly microporous carbons have been synthesized from four types of agro-wastes of lignin, walnut shells, orange peels and apricot seeds by one-step carbonization/activation with potassium hydroxide (KOH) in varying ratios. The resultant carbons demonstrated BET specific surface areas of 727-2254 m(2)/g, and total pore volumes 0.34-1.14 cm(3)/g. These are higher than the majority of agro-waste derived carbons reported in the literature. For all the carbons, CO2 adsorption at 298 K was higher than SF6 followed by N-2 suggesting a possible separation of CO2 and SF6 from N-2. The adsorbed amounts of CO2 at 298 K and 273 K and at pressures up to 760 Torr were 7.24 and 9.4 mmol/g, respectively which, to the best of our knowledge, are the highest CO2 uptakes in these temperatures by any carbon material reported so far. For all the gases, selectivity, mixed adsorption isotherms and adsorption breakthrough have been simulated from experimental data.