EXPLORATORY COSTS

12 Months Ended

Dec. 31, 2017

The following table sets forth capitalized exploratory well costs and includes additions pending determination of proved reserves, reclassifications to proved reserves and costs charged to expense:



Years ended December 31, (in thousands)	2017			2016			2015
Capitalized exploratory well costs at beginning of period	$	164,996		$	103,588		$	119,439
Additions pending determination of proved reserves	666,282			344,045			634,908
Reclassifications due to determination of proved reserves	(699,078		)	(282,637		)	(650,759		)
Capitalized exploratory well costs at end of period	$	132,200		$	164,996		$	103,588

The following table sets forth capitalized exploratory wells costs:



(in thousands)	December 31, 2017		December 31, 2016
Exploratory wells in progress (drilling rig not released)	$	10,879	$	14,531
Capitalized exploratory well costs for a period of one year or less	121,321		143,602
Capitalized exploratory well costs for a period greater than one year	—		6,863
Total capitalized exploratory well costs	$	132,200	$	164,996

At December 31, 2017, Energen had 49 gross exploratory wells either drilling or waiting on results from completion and testing in the Permian Basin. No wells were capitalized for a period greater than one year as of December 31, 2017.