Liquid oxygen, when heated, undergoes a phase transition and transforms into gaseous oxygen. This process is known as vaporization or evaporation. As the temperature of liquid oxygen increases, the molecules gain kinetic energy and start to move faster, breaking the intermolecular forces holding them together. As a result, the liquid oxygen molecules escape into the gas phase and become gaseous oxygen.

The boiling point of liquid oxygen at sea level is -183°C (-297.3°F). At this temperature, liquid oxygen transitions into gaseous oxygen under normal atmospheric pressure. However, if the liquid oxygen is heated above its boiling point, the vaporization process accelerates, and more oxygen gas is produced.

It is important to note that heating liquid oxygen requires careful handling and safety precautions due to its extremely cold temperature and its tendency to become a powerful oxidizer when in contact with organic materials.