Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2015

Property, Plant And Equipment [Abstract]

Schedule of Property, Plant and Equipment

	December 31, 2015				December 31, 2014
(Thousands of dollars)	Cost		Net		Cost	Net
Exploration and production1	$	21,607,962	9,723,222	2	22,731,220	13,277,985	2
Corporate and other		134,596	95,143		103,351	53,062
	$	21,742,558	9,818,365		22,834,571	13,331,047
1  Includes mineral rights as follows:	$	1,075,040	612,518		924,253	410,482

Net Changes in Capitalized Exploratory Well Costs

(Thousands of dollars)	2015		2014	2013
Beginning balance at January 1	$	120,455	393,030	445,697
Additions to capitalized exploratory well costs pending the      determination of proved reserves		64,578	2,874	57,716
Reclassifications to proved properties based on the      determination of proved reserves		–	(91,236)	(93,936)
Reduction of capitalized exploratory well costs due to      partial asset sale in Malaysia		–	(122,175)	–
Capitalized exploratory well costs charged to expense		(54,519)	(62,038)	(16,447)
Ending balance at December 31	$	130,514	120,455	393,030

Aging of Capitalized Exploratory Well Costs

	2015				2014				2013
(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	$	66,032	7	6	$	–	–	–	$	56,499	3	1
One to two years		–	–	–		59,330	3	1		60,787	7	1
Two to three years		57,876	3	–		6,606	3	–		–	–	–
Three years or more		6,606	3	–		54,519	2	2		275,744	22	7
	$	130,514	13	6	$	120,455	8	3	$	393,030	32	9

Schedule of Recognized Impairments

	December 31,
(Thousands of dollars)		2015	2014		2013
Gulf of Mexico	$	328,982	14,267		–
Western Canada – Heavy Oil		683,574	37,047	*	21,587
Malaysia		1,480,600	–		–
	$	2,493,156	51,314		21,587

*  This amount represented the writeoff of goodwill associated with an oil and gas company acquired in 2000.