The hydrogenation of CO is heterogeneously catalysed by ruthenium, rhodium, cobalt or iron (on silica); all four metals give largely n-1-alkenes as primary products, only small amounts of oxygenates are produced. The reactions already occur at temperatures greater than or equal to150 degreesC and pressures of syngas greater than or equal to1 atm, and mechanisms have been analysed [J. Am. Chem. Soc. 124 (2002) 10456]. In complete contrast, workers have shown that the hydrogenation of CO in solution by soluble cobalt, rhodium or ruthenium complexes, is much more demanding (temperatures greater than or equal to230 degreesC and pressures of syngas greater than or equal to400 atm) and leads to oxygenates (methanol, ethanol, ethylene glycol, and formates) and virtually no hydrocarbons. A few promoted systems give both, probably formed by independent paths. Reasons for this diversity are discussed. (C) 2003 Elsevier Science B.V. All rights reserved.