Crystallization studies have been conducted on three copolymers of propylene with ethylene as a function of supercooling at atmospheric pressure. The results confirm the conclusions reached almost 30 years ago that copolymerization causes the gamma-phase to be generated at atmospheric pressure for high molecular weight polymers. The greater the amount of comonomer, the greater the ease of formation of the gamma-phase. The gamma/alpha ratio is inversely proportional to supercooling, as has been found for isobaric crystallization at elevated pressures. It has been found that the equilibrium melting point decreases with ethylene content in a significant manner.