However, in the presence of a catalyst and at high temperatures, the oxygen produced reacts with carbon-based materials, such as methane or coal, to produce carbon monoxide:

The steam reforming reaction is as follows:

Cracked steam, also known as cracked gas or synthesis gas, is a mixture of gases produced by the thermal decomposition of steam (H2O) into its component elements, hydrogen (H2) and oxygen (O2), and carbon monoxide (CO). This process is known as steam cracking.