Exploratory Costs

The Company capitalizes exploratory well and project costs until a determination is made that the well or project has either found proved reserves, is impaired or is sold. The Company's capitalized exploratory well and project costs are presented in proved properties in the accompanying consolidated balance sheets. If the exploratory well or project is determined to be impaired, the impaired costs are charged to exploration and abandonments expense.

The following table reflects the Company's capitalized exploratory well and project activity during the three months ended March 31, 2014:



	Three Months Ended March 31, 2014
	(in millions)
Beginning capitalized exploratory costs	$	159
Additions to exploratory costs pending the determination of proved reserves	307
Reclassification due to determination of proved reserves	(210		)
Impairment of properties	(7		)
Exploratory well costs charged to exploration expense	(1		)
Ending capitalized exploratory costs (a)	$	248

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(a)	Includes $60 million of capitalized exploratory well costs classified as held for sale in the accompanying consolidated balance sheet as of March 31, 2014.

The following table provides an aging, as of March 31, 2014 and December 31, 2013, of capitalized exploratory costs and the number of projects for which exploratory costs have been capitalized for a period greater than one year based on the date drilling was completed:



	March 31, 2014		December 31, 2013
	(in millions, except project counts)
Capitalized exploratory costs that have been suspended:
One year or less	$	211	$	116
More than one year	37		43
	$	248	$	159

Number of projects with exploratory costs that have been suspended for a period greater than one year	1		1

Alaska - Nuna. The Company's Nuna project, which had $37 million of suspended project costs as of March 31, 2014, includes the Nuna-1 exploration well that was drilled during 2012 to test the Torok formation and a second appraisal well that was drilled and logged during the first quarter of 2013. The Company flow-tested the Nuna-1 well during the second quarter of 2012 and again in the first quarter of 2013. The second appraisal well encountered a mechanical problem and could not be flow-tested before the end of the winter drilling season. The results of the flow tests on the Nuna-1 well and the log data from the second Nuna well were both very encouraging. Prior to the sale of Pioneer Alaska, the Company was conducting a front-end engineering design study to evaluate the potential for onshore production facilities to support the project. The capitalized exploratory well costs associated with the Nuna project are classified as held for sale in the accompanying consolidated balance sheet as of March 31, 2014. See Note C for additional information about the Company's sale of Pioneer Alaska.