THE PROXIMATE ANALYSIS OF COAL WAS DEVELOPED AS A SIMPLE means of determining the distribution of products obtained when the coal sample is heated under specified conditions. As defined by ASTM D 121, proximate analysis separates the products into four groups: (1) moisture, (2) volatile matter, consisting of gases and vapors driven off during pyrolysis, (3) fixed carbon, the nonvolatile fraction of coal, and (4) ash, the inorganic residue remaining after combustion. Proximate analysis is the most often used analysis for characterizing coals in connection with their utilization. Differences in the type of information required by coal producers and consumers have led to variations in the kind and number of tests included under the rubric proximate analysis. Other terms used in the coal industry are short prox and prox.Commonusage in the field tends to favor short prox, which is the determination of moisture, ash, Btu, and sulfur, while prox means the determination of moisture, ash, volatile matter, fixed carbon, Btu, and sulfur. Proximate analysis as defined by ASTM International is the topic of this section.