Property, Plant and Equipment (Tables)

9 Months Ended

Sep. 30, 2017

Property, Plant And Equipment [Abstract]

Net Changes in Capitalized Exploratory Well Costs

(Thousands of dollars)	2017		2016
Beginning balance at January 1	$	148,500	130,514
Additions pending the determination of proved reserves		51,614	847
Reclassifications to proved properties based on the determination of proved reserves		(13,370)	–
Capitalized exploratory well costs charged to expense		(8,360)	–
Other adjustments		–	(3,205)
Balance at September 30	$	178,384	128,156

Aging of Capitalized Exploratory Well Costs

		September 30,
	2017				2016
(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	$	41,609	3	2	$	10,563	2	2
One to two years		8,430	2	2		53,101	3	3
Two to three years		43,197	1	1		31,627	2	–
Three years or more		85,148	7	1		32,865	4	–
	$	178,384	13	6	$	128,156	11	5