A pressure-controlled scanning calorimeter (PCSC) has been applied for measuring the isobaric volume thermal expansivities (alpha(p)) of crystalline polymers as a function of pressure up to 300 MPa at various temperatures. The measurements have been performed for several well-defined polyethylenes with various degrees of crystallinity at 302.6, 333.0, 362.6, and 393.0 K. The results are reported as values of coefficients in a correlation equation, which facilitates the use of reported data over large ranges of temperature and pressure. The general pressure-temperature behavior of alpha(p) for all polyethylenes under study is such that alpha(p) increases with temperature and decreases with pressure. The increase with temperature is smaller at high pressures and the isotherms of alpha(p) have a tendency to converge at high pressures; alpha(p) decreases linearly with the crystallinity of the polyethylene over the whole range of pressure and temperature under investigation. From the linear approximation of experimental data for polyethylenes with various crystallinities the estimated alpha(p) for both crystal and amorphous phases of polyethylenes have been determined as a function of pressure up to 300 MPa at 302.6, 333.0, and 362.5 K. The obtained results have been compared with available literature crystallographic data and with the values derived from the Pastine theoretical equation of state for both crystalline and amorphous phases.