We report a facile method for obtaining extremely high surface area and uniformly porous carbon nanofibers for supercapacitors. Blends of polyacrylonitrile and sacrificial Nafion at different compositions have been electrospun into non-woven nanofiber mats with diameters in the range of 200-400 nm. Electrospun nanofiber mats are then subjected to carbonization to obtain porous carbon nanofibers (CNFs) as polyacrylonitrile converts to carbon and Nafion decomposes out creating intra-fiber pores. Resultant porous CNFs exhibit specific surface area of up to 1600 m(2) g(-1) with a large fraction of mesopores (2-4 nm). No additional chemical or physical activation process was used. We demonstrate the tunability of the pore sizes within CNFs by varying the amount of Nafion. The non-woven fiber mats of porous CNFs are studied as free-standing electrode materials for supercapacitors eliminating the need for polymeric binding agents. Electrochemical measurements showed large specific gravimetric and volumetric capacitances of up to 210 F g(-1) and 60 F cm(-3) in 1 M H2SO4 at a high cyclic voltammetry scan rate of 100 mV s(-1) due to the large fraction of mesopores. These materials retain 75% performance at a large current density of 20 A g(-1) indicating excellent power handling capability. (C) 2013 Elsevier B.V. All rights reserved.