We report molecular dynamics simulations of liquid and amorphous Se at pressures from 0 to 6 GPa for different quench rates. The atomic volume depends strongly on the quench rate, in contrast to the small variation of the atomic enthalpy. The glass transition temperature Tg, extrapolated to a quench rate of order K/s, agrees within 20% with experiment. Applying a pressure of 1 GPa, Tg is raised by 37 K.