A comparison of the heating values and compositions of the raw product gases from selected coal gasification processes is shown in Table 9.4. Some of these processes, a few of which are used for synthesis gas production, have been commercialized. Some have been developed to the point where they might be termed near-commercial, and a few are under development. It is evident that a wide range of gas compositions can be produced by coal gasification. It is also evident that several of the gas compositions and operating conditions can be correlated with thermodynamic principles and the thermodynamics of the carbon-oxygen-steam system. Methane and carbon dioxide yields are generally higher at lower temperatures and higher pressures, as illustrated by the raw gas compositions for the Synthane process, whereas higher temperatures and lower pressures favor carbon monoxide and hydrogen, as illustrated by the raw gas compositions reported for the Koppers-Totzek process. Interestingly, the heating values of the product gases for processes supplied with steam — oxygen coreactants are generally in the same range despite the wide range of operating conditions. The heating values of the product gases from processes supplied with steam-air coreactants are also in the same range, although they are lower than those of the product gases produced by coal-steam-oxygen processes. Arithmetic adjustment of the heating values by deducting nitrogen from the product gases shows that all of them are in the same range.