Despite increasing efforts by major energy consumers to replace coal with cleaner fuels, volatile prices for other commodities like liquefied natural gas (LNG) have helped keep coal competitive for leading suppliers.

In the latest case of high gas prices creating a boon for coal suppliers, Glencore plc reported Tuesday that 2021 brought overwhelming results for its coal business despite a slight slip in volumes.

Global demand for thermal coal sent prices for the commodity soaring toward the end of the year. The company saw preliminary coal earnings at $900 million in the first six months of the year, but took in $4.3 billion in the last six months thanks to the spike. Prices for Newcastle thermal coal were up by an average of 125% year/year in 2021.

Along with supply constraints and...