Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2018

Property, Plant And Equipment [Abstract]

Schedule of Property, Plant and Equipment

	December 31, 2018				December 31, 2017
(Thousands of dollars)	Cost		Net		Cost	Net
Exploration and production1	$	22,629,844	9,654,945	2	20,329,930	8,120,293	2
Corporate and other		193,471	102,619		170,842	99,738
	$	22,823,315	9,757,564		20,500,772	8,220,031
1  Includes unproved mineral rights as follows:	$	512,025	144,912		600,423	198,349

2.  Includes $32,071 in 2018 and $38,670 in 2017 related to administrative assets and support equipment.

Schedule of Recognized Impairments

	December 31,
(Thousands of dollars)		2018	2017	2016
US Onshore (Midland)	$	20,000	–	–
Canada		–	–	95,088
Malaysia		–	–	–
	$	20,000	–	95,088

Net Changes in Capitalized Exploratory Well Costs

(Thousands of dollars)	2018		2017	2016
Beginning balance at January 1	$	175,640	148,500	130,514
Additions pending the determination of proved reserves		60,179	51,488	17,986
Reclassifications to proved properties based on the      determination of proved reserves		(2,214)	(15,988)	–
Capitalized exploration well costs charged to expense		(4,521)	(8,360)	–
Ending balance at December 31	$	229,084	175,640	148,500

Aging of Capitalized Exploratory Well Costs

	2018				2017				2016
(Thousands of dollars)	Amount		No. of Wells	No. of Projects	Amount		No. of Wells	No. of Projects	Amount		No. of Wells	No. of Projects
Aging of capitalized well   costs:
Zero to one year	$	61,096	1	1	$	41,480	3	2	$	20,481	1	1
One to two years		40,523	3	2		5,812	1	1		63,527	5	5
Two to three years		–	–	–		43,200	2	2		–	–	–
Three years or more		127,465	6	3		85,148	7	1		64,492	6	–
	$	229,084	10	6	$	175,640	13	6	$	148,500	12	6