Very little emphasis has been directed towards UCG product gas cleanup and upgrading because the greatest uncertainties have been and remain with the underground process. Although much applicable surface process experience is available from surface gasification and syngas conversion facilities, UCG gas cleanup has some uniqueness. The raw product gas from an underground coal gasification process will emerge from the product wells near 600 degrees F and contain particulates, trace metals, alkali, sulfur and nitrogen compounds, carbon dioxide, condensable hydrocarbons, and moisture. These by-products must be sufficiently removed to ensure reliable operation of the gas gathering and preparation train for the power generation equipment or the chemical conversion facility. The product gas end use will affect the severity and nature of the cleanup requirements.