Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant And Equipment [Abstract]

Schedule of Property, Plant and Equipment

	December 31, 2017				December 31, 2016
(Thousands of dollars)	Cost		Net		Cost	Net
Exploration and production1	$	20,329,930	8,120,293	2	20,767,772	8,214,740	2
Corporate and other		170,842	99,738		156,231	101,448
	$	20,500,772	8,220,031		20,924,003	8,316,188
1  Includes unproved mineral rights as follows:	$	600,423	198,349		595,138	188,689

2.  Includes $38,670 in 2017 and $48,053 in 2016 related to administrative assets and support equipment.

Schedule of Recognized Impairments

	December 31,
(Thousands of dollars)		2017	2016	2015
Gulf of Mexico	$	–	–	328,982
Canada		–	95,088	683,574
Malaysia		–	–	1,480,600
	$	–	95,088	2,493,156

Net Changes in Capitalized Exploratory Well Costs

(Thousands of dollars)	2017		2016	2015
Beginning balance at January 1	$	148,500	130,514	120,455
Additions pending the determination of proved reserves		51,488	17,986	64,578
Reclassifications to proved properties based on the      determination of proved reserves		(15,988)	–	–
Capitalized exploratory well costs charged to expense		(8,360)	–	(54,519)
Ending balance at December 31	$	175,640	148,500	130,514

Aging of Capitalized Exploratory Well Costs

	2017				2016				2015
(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	$	41,480	3	2	$	20,481	1	1	$	66,032	7	6
One to two years		5,812	1	1		63,527	5	5		–	–	–
Two to three years		43,200	2	2		–	–	–		57,876	3	–
Three years or more		85,148	7	1		64,492	6	–		6,606	3	–
	$	175,640	13	6	$	148,500	12	6	$	130,514	13	6