Results of 100 MHz H-1 NMR study of melt condensation of ortho-and paramethylolphenol mixture in different catalytic conditions and in the presence of phenol are presented. Reaction rate and chemical composition of intermediates and polycondensates are the main points highlighted. Two different mechanisms for alkali-catalyzed condensation and for condensations in other catalytic conditions have been ascertained. The co-condensation rate is dependent mainly on methylolphenol reactivity and catalyst, and is similar in reactions with phenol and with the most abundant component of oil shale alkylresorcinols-5-methylresorcinol.