The conversion of guaiacol catalyzed by Pt/MgO in the presence of H-2 was investigated with a flow reactor at 573 K and 140 kPa. Among the dozens of reaction products identified by gas chromatography (GC) and GC/mass spectrometry, the predominant ones were phenol, catechol, and (surprisingly) cyclopentanone, with others including methane, n-butane, butenes, n-pentane, and carbon monoxide. The predominant reactions were hydrodeoxygenation (with about 70 % of the guaiacol that was converted forming products that were reduced in oxygen). In contrast, when the catalyst incorporated an acidic support, Pt/gamma-Al2O3, other reactions became kinetically significant, exemplified by transalkylation, and the selectivity to deoxygenated products was reduced to about half the value observed with Pt/MgO at guaiacol conversions in the range of about 6-20 %. Pt/MgO underwent deactivation less rapidly than Pt/gamma-Al2O3, consistent with a lower rate of coke formation and with observations by scanning transmission electron microscopy showing that the average platinum cluster diameter, approximately 1-2 nm in each catalyst, did not change significantly during operation. The results point to the advantages of basic supports for noble metal hydrodeoxygenation catalysts. .