Formaldehyde reacts with solvents that contain hydroxyl groups (R-OH) in oligomerization reactions to oxymethylene oligomers (R-(OCH2)(n)-OH). The chemical equilibria of these reactions have been studied in the literature for water, for the mono-alcohols methanol, ethanol, and 1-butanol, as well as for the diols ethylene glycol and 1,4-butynediol. In the present work, the collective data were analyzed. It was found that the prolongation of the oxymethylene chains by the addition of formaldehyde can be described very well with a generalized chemical equilibrium constant K-x,n >= 2(R-OH), which is independent of the substructure (R) of the solvent. This holds for the oligomerization reactions leading to R-(OCH2)(n)-OH with n >= 2. The chemical equilibrium constantK(x,1)(R-OH) of the reaction of formaldehyde with the solvent R-OH depends on the solvent, but simple trends are observed. The hypotheses of the existence of a generalized chemical equilibrium constant K-x,n >= 2(R-OH) was tested for the reactions of formaldehyde with ethanol and 1-propanol, for which neither K-x,12(R-OH) nor K-x,n(R-OH) was previously available. The corresponding equilibria were studied by C-13 NMR spectroscopy and the equilibrium constants were determined. A novel method was developed and used in these studies to obtain data on K(x,1)(R-OH)by NMR spectroscopy, which is difficult because of the low amount of molecular formaldehyde. It was found that the generalized equilibrium constant is even valid for the acid-catalyzed formation of poly(oxymethylene) dimethyl ethers (OME).