Property, Plant and Equipment (Tables)

6 Months Ended

Jun. 30, 2016

Property, Plant And Equipment [Abstract]

Net Changes in Capitalized Exploratory Well Costs

(Thousands of dollars)	2016		2015
Beginning balance at January 1	$	130,514	120,455
Additions pending the determination of proved reserves		800	1,620
Other adjustments		(3,205)	–
Balance at June 30	$	128,109	122,075

Aging of Capitalized Exploratory Well Costs

		June 30,
	2016				2015
(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	$	63,617	5	5	$	217	2	1
One to two years		–	–	–		32,192	2	1
Two to three years		31,627	2	–		27,842	2	–
Three years or more		32,865	4	–		61,824	4	2
	$	128,109	11	5	$	122,075	10	4