Because of less coal consumption as well as coal capacity retirements over the past three years, the days of burn of U.S. coal remain within the typical range, even though total stocks are low. For bituminous coal plants, largely located in the eastern United States, the average number of days of burn was 88 days in September, a slight increase from the 86 days of burn recorded in August. The average number of days of burn for subbituminous units, most of which are in the western United States, was 82 days in September 2021.

Given the long-term trend of declining coal consumption, many U.S. mines have begun to close. Reduced production capacity and supply chain disruptions have created some concerns about the ability of coal-fired generators to replenish stockpiles to last through the winter (October–March).

Electric grid operators are closely monitoring coal inventories this winter. PJM, the grid operator for the largest electric system in the United States, instituted temporary changes to rules governing minimum inventory requirements to provide more flexibility for coal-fired generators, given low stockpiles at some plants and supply chain disruptions.