The Oil Drum

It depends under what conditions they are mining. In many room and pillar mining operations, after they have reached the boundary of the working, then they try and recover part of the coal from the pillars as they retreat back out. Obviously it is a tricky game to ensure you leave enough to be safe while doing it, yet getting out the most that you can. It has been helped in the recent past by the introduction of remotely operated artificial ground supports (like the shields from the longwall models). It also depends on the Safety Factor used in the design and while the global average for underground is around 50% recovery with the right conditions, equipment and supervision room and pillar can approach longwall in the amount of coal recovered. I checked here and was amused, apropos the post, to see that they don't count coal thinner than 42 inches as a reserve.

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