Capitalized Exploratory Well Costs and Undeveloped Leasehold Costs (Tables)

9 Months Ended

Sep. 30, 2018

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, 2018
Capitalized Exploratory Well Costs, Beginning of Period	$	520
Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves	7
Divestitures ⁽¹⁾	(168		)
Reclassified to Proved Oil and Gas Properties Based on Determination of Proved Reserves	(1		)
Capitalized Exploratory Well Costs Charged to Expense	—
Capitalized Exploratory Well Costs, End of Period	$	358

⁽¹⁾

Represents costs primarily related to Gulf of Mexico assets.

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



(millions)	September 30, 2018		December 31, 2017
Exploratory Well Costs Capitalized for a Period of One Year or Less	$	8	$	10
Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling	350		510
Balance at End of Period	$	358	$	520
Number of Projects with Exploratory Well Costs That Have Been Capitalized for a Period Greater Than One Year Since Commencement of Drilling	7		8