The physicochemical and kinetic properties of resols prepared with different catalysts (NaCH, LiOH and Ba(OH)(2)) and variable formaldehyde/phenol ratios (2.5 pound R pound 3.5) were followed to determine their effects on the mechanisms and reaction products at a fixed pH and temperature. Kinetic monitoring and quantification of residual monomers were carried out by liquid chromatography coupled with mass spectrometry (LC/UV/MS), by C-13 nuclear magnetic resonance (NMR) and by chemical assay for formaldehyde. Oligomer formation (n : 2) was determined by LC/LTV/MS, size exclusion chromatography (SEC) and C-13 NMR. It was found that minor compounds form during syntheses (phenol methanol hemiacetals, hemiacetals of phenol and of oligomers...) and that the ratio R affects primarily the kinetics of formation of monomers and oligomers, in contrast to the catalysts that modify reaction mechanisms. The understanding of the structure of the resols was an important step for the determination of the final properties of the material