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:



	Three months ended June 30,
(in thousands)	2017			2016
Capitalized exploratory well costs at beginning of period	$	168,265		$	105,591
Additions pending determination of proved reserves	170,737			78,457
Reclassifications due to determination of proved reserves	(197,601		)	(146,610		)
Capitalized exploratory well costs at end of period	$	141,401		$	37,438



	Six months ended June 30,
(in thousands)	2017			2016
Capitalized exploratory well costs at beginning of period	$	164,996		$	103,588
Additions pending determination of proved reserves	335,703			161,903
Reclassifications due to determination of proved reserves	(359,298		)	(228,053		)
Capitalized exploratory well costs at end of period	$	141,401		$	37,438

The following table sets forth capitalized exploratory well costs:



(in thousands)	June 30, 2017		December 31, 2016
Exploratory wells in progress (drilling rig not released)	$	15,224	$	14,531
Capitalized exploratory well costs capitalized for a period of one year or less	126,177		143,602
Capitalized exploratory well costs for a period greater than one year	—		6,863
Total capitalized exploratory well costs	$	141,401	$	164,996