The outgassing characteristic of an ordinary stainless-steel ultrahigh vacuum (UHV) chamber was determined using an extremely dry nitrogen venting system, and compared with that of an extreme high vacuum (XHV) chamber. A marked sorption resistance effect of the vacuum surface of the XHV chamber was found. The outgassing rate of the XHV chamber was about 100 times lower than that of the ordinary UHV chamber in the unbaked case. It is believed that the recent achievement of fast pumpdown to UHV is the result of not only the reduction of the water content of the venting gas, but also the low gas-sorability of the vacuum surface.