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Supplemental Coal Data (unaudited) (Tables)
 12 Months Ended
Dec. 31, 2019
Mineral Industries Disclosures [Abstract]  
Schedule of Proven and Probable Reserves Rollforward
Supplemental Coal Data (unaudited)
 
 
Millions of Tons
 
 
For the Year Ended December 31,
 
 
2019
 
2018
 
2017
 
2016
 
2015
Consolidated recoverable coal reserves at beginning of period
 
2,261

 
2,298

 
2,361

 
3,047

 
3,238

Purchased reserves
 
—

 
—

 
—

 
—

 
24

Reserves sold in place
 
—

 
—

 
(16
)
 
(601
)
 
(43
)
Production
 
(27
)
 
(28
)
 
(26
)
 
(26
)
 
(29
)
Revisions and other changes
 
(8
)
 
(9
)
 
(21
)
 
(59
)
 
(143
)
Consolidated recoverable coal reserves at end of period* (1)
 
2,226

 
2,261

 
2,298

 
2,361

 
3,047

______________
* Recoverable coal reserves are the equivalent of “demonstrated reserves” under the coal resource classification system of the U.S. Geological Survey. Generally, these reserves would be commercially mineable at year-end prices and cost levels, using current technology and mining practices.
(1) 143.3 million tons of the Northern Appalachia product are controlled by CCC, a former subsidiary of the Company's former parent that was sold in December 2013. As of this filing, these tons are still controlled by CCC but are shown in CONSOL Energy's reserves due to a binding agreement that these tons will be released to CONSOL Energy upon the assignment of the underlying lease to CONSOL Energy.