The invention provides a method of making a copolyester and a resulting copolyester fiber that has increased dyeability and dye retention properties while maintaining good physical properties for textile applications. The fiber may be formed from a mixture comprising terephthalic acid and its ester equivalent in combination with ethylene glycol, and to which is added about 2-4 mole percent of at least two dicarboxylic acids, or their anhydride or ester equivalents excluding terephthalic acid and its ester equivalent, and between about 100 to 700 ppm pentaerytoritol, both being based on the amount of the terephthalic acid and its ester equivalent The dicarboxylic acids and pentaerytliritol may be added before esterification, or after esterification and before polycondensation.