In this paper a statistical derivation is presented for the weight average molecular weight of high polymers without having to know the molecular size distribution func-tions．As gelation Occurs when Mw→∞ the critical conditions of gelation can be calcu-lated by a simple but generalized method． By using the new method，the gel points of reactions of various types have been computed．According to this method，the results previously obtained by the present authors and others are only a few special cases．Other important types of reactions which seem very complicated，such as esterification or amination by organic acid anhydrides or a mixture of various poly—basic acids，ring opening reaction of epoxides，phenol-formaldehyde reaction and addition polymerization of divinyl monomers have also been considered． Effects of intramolecular reaction (cyclization) are discussed． It is suggested that if we replace the total degree of reaction by a partial quantity that is the degree of reaction between molecules，cyclizations do not alter the critical conditionS of gelation．