We report results on the physisorption of N2 and H2 at low temperatures by single-walled carbon nanotubes (SWNTs) produced by the arc discharge method. We characterized (SEM, TEM, and HRTEM characterizations) two batches of sample, raw collaret and chemically treated SWNTs, in order to determine the best nanotube-containing sample for gas storage. Treatments and the effectiveness of the chemical acid treatments are discussed. Adsorption measurements of N2 on SWNTs allow us to obtain the specific surface area and pore size distribution. Acid treatments used to purify and open (by cutting) nanotubes decreased the surface area as a result of material compaction. Measurements of H2 adsorption were performed in order to evaluate the adsorption capacity of the nanotubes at 133K and below 2 bar. We found up to H:C atomic ratio=0.35, ie. 2.4 wt% of adsorbed hydrogen by gram of sample for our raw material.