Solution spun polyacrylonitrile (PAN), PAN/multi-wall carbon nanotube (MWCNT), and PAN/single-wall carbon nanotube (SWCNT) fibers containing 5 wt.% carbon nanotubes were stabilized in air and activated using CO2 and KOH. The surface area as determined by nitrogen gas adsorption was an order of magnitude higher for KOH activated fibers as compared to the CO2 activated fibers. The specific capacitance of KOH activated PAN/SWCNT samples was as high as 250 F g(-1) in 6 M KOH electrolyte. Under the comparable KOH activation conditions, PAN and PAN/SWCNT fibers had comparable surface areas (BET surface area about 2200 m(2) g(-1)) with pore size predominantly in the range of 1-5 nm, while surface area of PAN/MWCNT samples was significantly lower (BET surface area 970 m(2) g(-1)). The highest capacitance and energy density was obtained for PAN/SWCNT samples, suggesting SWCNT advantage in charge storage. The capacitance behavior of these electrodes has also been tested in ionic liquids, and the energy density in ionic liquid is about twice the value obtained using KOH electrolyte. (C) 2008 Elsevier B.V. All rights reserved.