Lean and rich premixed flames of three different C-3-oxygenated hydrocarbons (acetone, n-propanol, and i-propanol) at low pressure have been investigated with tunable synchrotron photoionization and molecular-beam mass spectrometry. Flame species, including isomeric intermediates, are unambiguously identified with measurements of photoionization efficiency spectra by scanning the photon energy. Mole fraction profiles of most observed species are measured by scanning the burner position at selected photon energies near ionization thresholds, and the flame temperature profiles are recorded using a Pt/Pt-13%Rh thermocouple. Compared with previous studies, some new flame species, e.g., vinyl, propargyl, ally], ethenol, methyl ketene, propenols, ethyl ketene, methyl ethyl ketone, butenols, and 1,3,5-hexatriyne, are detected in this work, which will extend our knowledge of the intermediate pools of oxygenated hydrocarbon combustion. On the other hand, comparisons among chemical structures of these flames have been performed, based on the comprehensive experimental data. It is concluded that different structural features of fuel molecules will cause a lot of variation in intermediate pools, isomeric compositions, and formation channels of flame species, especially for the oxygenated intermediates. Combined with previous research on hydrocarbon flames, analyses of pollutant emissions and soot formation are presented. It is consistent with previous studies that the oxygenated fuels have reduced sooting tendencies and potential emissions of toxic oxygenated by-products. (C) 2007 The Combustion Institute. Published by Elsevier Inc. All rights reserved.