An apparatus for the determination of the solubility of gases in polymers at high pressure and high temperature is described. The solubilities of nitrogen in low-density polyethylene (PE800E) at 394-450 K at pressures between 10 and 125 atm are reported. Empirical correlations are obtained which represent the Flory-Huggins interaction parameter chi, solubility coefficient K-H, and activity coefficient of dissolved gas Ohm(2) as functions of temperature and pressure for the above system.