The following summarizes the changes in suspended exploratory well costs at December 31 for each of the last three years. Additions pending the determination of proved reserves excludes amounts capitalized and subsequently charged to expense within the same year.


millions	2012		2011		2010
Balance at January 1	$	1,353	$	935	$	579
Additions pending the determination of proved reserves		960		572		491
Reclassifications to proved properties		(129)		(116)		(106)
Charges to exploration expense		(122)		(38)		(29)
Balance at December 31	$	2,062	$	1,353	$	935

The following summarizes an aging of suspended exploratory well costs by geographic area and the year the costs were suspended at December 31, 2012:


			Year Costs Incurred
									2009 and
millions	Total		2012⁽¹⁾		2011		2010		prior
United States—Onshore	$	136	$	123	$	3	$	—	$	10
United States—Offshore		392		158		(5)		61		178
International		1,534		636		396		314		188
	$	2,062	$	917	$	394	$	375	$	376

(1) Excludes additions subsequently reclassified to proved properties within the same year.

Suspended exploratory well costs capitalized for a period greater than one year at December 31, 2012, after completion of drilling were associated with 22 projects, primarily located in Ghana, Brazil, the Gulf of Mexico, and Mozambique. Project costs suspended for longer than one year were primarily suspended pending the completion of economic evaluations including, but not limited to, results of additional appraisal drilling, facilities, infrastructure, well-test analysis, additional geological and geophysical data, development plan approval, and permitting. Management believes projects with suspended exploratory well costs exhibit sufficient quantities of hydrocarbons to justify potential development and is actively pursuing efforts to assess whether reserves can be attributed to these projects. If additional information becomes available that raises substantial doubt as to the economic or operational viability of any of these projects, the associated costs will be expensed at that time.