Abstract The solvent extraction equilibrium of boron extraction has been studied for petroleum ether, kerosene and chloroform solutions of 2-ethyl-1,3-hexanediol (EHD) and 2-chloro-4(1,1,3,3-tetramethylbutyl)-6-methylolphenol (CTMP or 3-chloro-5-(1,1,3,3-tetramethylbutyl)salicyl alcohol), employed both singly and in admixture. A theory has been proposed to explain the observed trends in extraction with changes in pH and organic reagent concentration. It was found that the extractions could be explained satisfactorily on the basis of this theory without involvement of numerous association reactions reported in the literature. According to the shapes of the plots of log D against pH and extractant concentration, the mode of extraction was similar in all three diluents despite differences in molecular mass and polarity, although, unlike that with CTMP, EHD extraction did not involve the sodium ion below pH 9.8. No enhancement of extraction, known as synergism, was observed when EHD and CTMP were used in admixture.