Property, Plant and Equipment (Tables)

3 Months Ended

Mar. 31, 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		–	141
Other adjustments		(886)	–
Balance at March 31	$	129,628	120,596

Aging of Capitalized Exploratory Well Costs

		March 31,
	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	$	65,136	7	6	$	–	–	–
One to two years		–	–	–		32,192	2	1
Two to three years		31,627	2	–		33,744	4	2
Three years or more		32,865	4	–		54,660	2	–
	$	129,628	13	6	$	120,596	8	3