(7) SUSPENDED EXPLORATORY WELL COSTS

We capitalize exploratory well costs until a determination is made that the well has either found proved reserves or that it is impaired. Capitalized exploratory well costs are presented in natural gas and oil properties in the accompanying consolidated balance sheets. If an exploratory well is determined to be impaired, the well costs are charged to exploration expense in the accompanying consolidated statements of operations.

The following table reflects the changes in capitalized exploratory well costs for the three months ended March 31, 2013 and the year ended December 31, 2012 (in thousands except for number of projects):


	March 31, 2013	December 31, 2012

Balance at beginning of period	$ 57,360	$ 93,388
Additions to capitalized exploratory well costs pending the determination of proved reserves	62,640	153,250
Reclassifications to wells, facilities and equipment based on determination of proved reserves	(58,601)	(184,298)
Divested wells	—	(4,980)

Balance at end of period	61,399	57,360
Less exploratory well costs that have been capitalized for a period of one year or less	(39,140)	(45,965)

Capitalized exploratory well costs that have been capitalized for a period greater than one year	$ 22,259	$ 11,395

Number of projects that have exploratory well costs that have been capitalized for a period greater than one year	9	5

As of March 31, 2013, $22.3 million of capitalized exploratory well costs have been capitalized for more than one year with six of the wells waiting on pipelines and three of the wells currently in the completion stage. Five of the wells are not operated by us and eight of the wells are in Pennsylvania. In first quarter 2012, we sold a seventy-five percent interest in an East Texas exploratory well. Refer to Note 4 for additional information.

The following table provides an aging of capitalized exploratory well costs that have been suspended for more than one year as of March 31, 2013 (in thousands):

	Total	2013	2012	2011	2010	2009	2008

Capitalized exploratory well costs that have been capitalized for more than one year	$ 22,259	$ 5,854	$ 5,961	$ 5,965	$ 72	$ 2,884	$ 1,523