Property, Plant and Equipment (Tables)

6 Months Ended

Jun. 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		48,764	800
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 June 30	$	175,534	128,109

Aging of Capitalized Exploratory Well Costs

		June 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	$	57,900	3	3	$	63,617	5	5
One to two years		53,023	3	3		–	–	–
Two to three years		–	–	–		31,627	2	–
Three years or more		64,611	6	–		32,865	4	–
	$	175,534	12	6	$	128,109	11	5