Subbituminous refers to a type of coal that is intermediate in rank between bituminous and sub-bituminous coals. It has a higher heating value, lower sulfur content, and lower moisture content compared to lignite or peat.
Production of subbituminous coal in Wyoming more than compensated for this decline in terms of volume and — according to its stated reserves — this trend can continue for another 10 to 15 years. (resilience.org)
Wyoming produces the vast majority of subbituminous coal in the U.S. (eia.gov)
By contrast, the share for subbituminous coal rose from 18 percent in 1980 to 25 percent in 1992, while the share for lignite grew from 6 percent to 9 percent. (eia.gov)