We applied the experimental technique of low energy (e,2e) spectroscopy in back-reflection geometry to measure the two-dimensional energy distributions of correlated electron pairs excited by 20 eV primary electrons from a clean and oxygen covered W(001) surface. For the first time the contribution of correlated electron pairs originating from two different W(001) surface states S-1 and S-2 was identified in the (e,2e) spectra, thus demonstrating the high surface sensitivity of low energy (e,2e) spectroscopy. It was found that the generation of electron pairs from W(001) surface states is considerably suppressed by the adsorption of 0.1 L of oxygen. The binding energies and the k(parallel to)-distributions of these states as determined in our measurements are in a reasonable agreement with the photoemission data, (C) 1998 Elsevier Science B.V. Ail rights reserved. [References: 16]