The absolute density, thermal expansion coefficient α, and thermal pressure coefficient γ have been determined for atactic polystyrene in the non-glassy liquid (or amorphous) state. Dilatometric measurements on the pure polymer furnished α over the range 100° to 230°C. Thermal pressure coefficients were determined by extrapolation from measurements on concentrated solutions of the polymer in benzene, from 24° to 100°C. No evidence was found for a second order transition above 100°C. A small change in dα/dT was observed near 170°C. This and other observations suggest a minor departure from equilibrium below this temperature.