Property, Plant and Equipment (Tables)

3 Months Ended

Mar. 31, 2019

Property, Plant And Equipment [Abstract]

Net Changes in Capitalized Exploratory Well Costs

(Thousands of dollars)	2019		2018
Beginning balance at January 1	$	207,855	155,103
Additions pending the determination of proved reserves		32,416	549
Capitalized exploratory well costs charged to expense		(13,145)	–
Balance at March 31	$	227,126	155,652

Aging of Capitalized Exploratory Well Costs

		March 31,
	2019				2018
(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	$	78,016	3	2	$	13,642	2	1
One to two years		–	–	–		27,757	1	1
Two to three years		27,270	1	1		49,642	2	2
Three years or more		121,840	5	1		64,611	6	–
	$	227,126	9	4	$	155,652	11	4