The incident occurred around 12.30pm local time, when workers hit a pocket of the gas while in a pit, according to local newspaper the Evansville Courier and Press.
The workers’ names and conditions have not been released, but the news outlet said one miner was taken away from the mine by ambulance and the other by helicopter.
A request for details and comment from the US Mine Safety and Health Administration was not returned by press time.
The Gibson County complex is owned by Black Beauty Coal, a subsidiary of Peabody Energy.
The Black Beauty complex includes both underground and surface operations which sold a combined 22.5 million tons of coal in 2006 and is the largest coal producer in the Illinois Basin.
As well as Somerville, Black Beauty also includes Farmersburg, Francisco, Air Quality, and Viking and Miller Creek, as well as the Vermilion Grove portal in eastern Illinois.
