Property, Plant and Equipment (Tables)

3 Months Ended

Mar. 31, 2021

Property, Plant and Equipment [Abstract]

Net Changes in Capitalized Exploratory Well Costs

The following table reflects the net changes in capitalized exploratory well costs during the three-month periods ended March 31, 2021 and 2020.

(Thousands of dollars)	2021		2020
Beginning balance at January 1	$	181,616	217,326
Additions pending the determination of proved reserves	785		816
Capitalized exploratory well costs charged to expense	—		(39,709)
Balance at March 31	$	182,401	178,433

Aging of Capitalized Exploratory Well Costs

The following table provides an aging of capitalized exploratory well costs based on the date the drilling was completed for each individual well and the number of projects for which exploratory well costs have been capitalized.  The projects are aged based on the last well drilled in the project.

	March 31,
	2021				2020
(Thousands of dollars)	Amount		No. of Wells	No. of Projects	Amount	No. of Wells	No. of Projects
Aging of capitalized well costs:
Zero to one year	$	—	—	—	24,637	3	3
One to two years	23,514		3	3	31,541	2	2
Two to three years	30,562		2	2	—	—	—
Three years or more	128,325		6	—	122,255	6	—
	$	182,401	11	5	178,433	11	5

Schedule of Recognized Impairments

The following table reflects the recognized impairments for the three months ended March 31, 2021 and 2020.

	Three Months Ended March 31,
(Thousands of dollars)	2021		2020
U.S.	$	—	927,821
Canada	171,296		—
Other Foreign	—		39,709
	$	171,296	967,530