The base version of the Coal Mine generates 1 Coal per Game tick. The capacity of the mine can be extended using 4 extension buildings that can be built on adjacent tiles to the base Coal Mine building. Three of the extensions provide a increase to the Coal output of the mine, of all extensions the "Second headframe" provides the largest increase to Coal production. The "Timber Tunnel Supports" extension adds a new process that consumes Timber while providing a large increase to Coal production. When all extensions are built around a Coal Mine, it consumes 0.5 Timber and produces 6 Coal Per Game tick.