Heat transfer and bubble characteristics (including bubble size, bubble rise velocity, and bubble formation frequency) from a nozzle in high-pressure bubble columns are studied. The experiments are conducted at pressures up to 15.2 MPa and temperature at 27 degrees C. As pressure increases, the bubble size and the bubble rise velocity decrease, but the bubble formation frequency increases in the bubbling regime. The effects of pressure on bubble characteristics are more significant at high nozzle gas velocities than at low nozzle gas velocities. The transition from the bubbling to the jetting is identified based on two methods: visualization and power spectra of the signals from a pressure transducer. The transition velocity from bubbling regime to jetting regime decreases with increasing pressure or temperature. In the bubbling regime, the heat transfer coefficient has a significant increase with increasing pressure and nozzle gas velocity. The higher the pressure, the larger the increasing rate of the heal transfer coefficient and the nozzle gas velocity. In the jetting regime, however, the influence of pressure on the heat transfer coefficient is small.