We have studied the CO hydrogenation over a Co/SiO2 catalyst under mild reaction conditions (up to 4.4 bar total pressure, H-2/CO = 2, T = 483 K) and performed a post-reaction analysis of the chemical surface composition by means of secondary ion mass spectrometry (SIMS) and temperature-programmed reaction (TPR) in hydrogen gas. A hydrocarbon chain growth probability alpha = 0.78 was found in the catalytic studies. The SIMS analysis revealed the existence of individually adsorbed CxHy species up to C8Hy, in accordance with end-on bonding to the catalyst surface. These species were removed from the catalyst surface in the subsequent H-2-TPR experiment. Significant methane desorption occurred at temperatures (greater than or equal to 500 K) well above those of the longer-chain hydrocarbons indicating either an increasing hydrogenolysis activity of Co metal during H-2-TPR or the presence of a more tightly bound "carbidic" adsorbate under FT conditions.