There are a variety of geologic conditions in the Appalachian coal field that bear on coal resources and reserves determinations. Sedimentary associations are the basic means of locating coal. An adequate measurement of coal thickness is still the primary consideration in the determination of coal-bed geometry. Strongly folded and thrust-faulted conditions have direct and often drastic effects on coal beds, making estimation of resources difficult. The gentle structure of the wide basin obscures beds at depth. Sedimentary models are useful for explaining and analyzing conditions, but thus far they have added little toward establishing precise coal-bed margins. Quality of coal-resources maps is directly dependent on the amount of data and the competency of the geologic interpretation. Splits, benches, and coals mapped in zones cause difficulties. Primary data in notebooks or core logs are often lost, thus necessitating remeasuring where needed and possible.