Adsorbents and methods for the adsorptive separation of para-xylene from a mixture containing at least one other C.sub.8 aromatic hydrocarbon (e.g., a mixture of ortho-xylene, meta-xylene, para-xylene, and ethylbenzene) are described. Suitable adsorbents comprise small-crystallite-size zeolite X having an average crystallite size of less than 1.8 microns. The adsorbents may be binderless (e.g., formulated with the substantial absence of an amorphous material that normally reduces selective pore volume) to further improve capacity and mass transfer. These properties are especially advantageous for improving productivity in low temperature, low cycle time adsorptive separation operations in a simulated moving bed mode.