(Solid + liquid) equilibria for the binary systems (N-methyl-2-pyrrolidinone + phenol, or 3,5-dimethylphenol) have been determined using a cryometric dynamic method. Congruently melting compounds form with the formulae: C5H9NO center dot C6H5OH, or C5H9NO center dot(C6H5OH)(2), and C5H9NO center dot C8H9OH, or C5H9NO center dot(C8H9OH)(2). Compound formation is attributed to a charge-transfer interaction of N-methyl-2-pyrrolidinone with phenol or 3,5-dimethylphenol, or is attributed to a strong O-(HO)-O-... hydrogen bond between the oxygen atom of N-methyl-2-pyrrolidinone and hydroxyl group of phenol. The larger intermolecular interaction is observed for the (N-methyl-2-pyrrolidinone + phenol) binary mixture, where the melting temperature of the 1:1 congruently melting compound is higher. Experimental solubility results are compared with values calculated by means of the Ott equation using parameters derived from the SLE results. The correlation of the solubility data is obtained with a average root-mean-square deviation in temperature sigma(T) = 0.25 K and sigma(T) = 0.19 K for the systems with phenol or 3,5-dimethylphenol, respectively. (c) 2005 Elsevier B.V All rights reserved.