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Exploratory Well Costs (Notes)
 12 Months Ended
Dec. 31, 2017
Capitalized Exploratory Well Costs [Abstract]  
Exploratory Well Costs
Exploratory Well Costs

EOG's net changes in capitalized exploratory well costs for the years ended December 31, 2017, 2016 and 2015 are presented below (in thousands):
 
2017
 
2016
 
2015
 
 
 
 
 
 
Balance at January 1
$
—

 
$
8,955

 
$
17,253

Additions Pending the Determination of Proved Reserves
27,487

 
6,688

 
24,640

Reclassifications to Proved Properties
(20,802
)
 
(5,274
)
 
(26,659
)
Costs Charged to Expense (1)
(4,518
)
 
(10,369
)
 
(6,279
)
Balance at December 31
$
2,167

 
$
—

 
$
8,955

 
(1)
Includes capitalized exploratory well costs charged to either dry hole costs or impairments.

At December 31, 2017, 2016 and 2015, all exploratory well costs had been capitalized for periods of less than one year.