Capitalized Exploratory Well Costs and Undeveloped Leasehold Costs (Tables)

9 Months Ended

Sep. 30, 2017

Changes in capitalized exploratory well costs are as follows and exclude amounts that were capitalized and subsequently expensed in the same period:



(millions)	Nine Months Ended September 30, 2017
Capitalized Exploratory Well Costs, December 31, 2016	$	768
Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves	10
Reclassified to Proved Oil and Gas Properties Based on Determination of Proved Reserves ⁽¹⁾	(203		)
Capitalized Exploratory Well Costs, September 30, 2017	$	575


⁽¹⁾	Amount relates to the approval and sanction of the first phase of development of the Leviathan field, offshore Israel. During second quarter 2017, we recorded Leviathan field proved undeveloped reserves of 551 MMBoe, net.

The following table provides an aging of capitalized exploratory well costs based on the date that drilling commenced:



(millions)	September 30, 2017		December 31, 2016
Exploratory Well Costs Capitalized for a Period of One Year or Less	$	11	$	69
Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling ⁽¹⁾	564		699
Balance at September 30, 2017	$	575	$	768


⁽¹⁾	The decrease from December 31, 2016 is attributable to the reclassification of the Leviathan field to development work in process, partially offset by the capitalization of interest during the period on remaining exploratory wells.