Note 5 – Property, Plant and Equipment

Net property, plant and equipment at December 31, 2018 and 2017 consists of the following:

(in thousands)	As of December 31,
	2018			2017

Oil and gas properties:
Proved oil and gas properties	$	347,059		$	114,893
Unproved properties not subject to depletion		5,416			1,947
Accumulated depreciation, depletion, amortization and impairment		(98,604	)		(80,715	)
Net oil and gas properties		253,871			36,125

Pipeline facilities and equipment		12,714			-
Base gas		2,122			-
Furniture and fixtures, computer hardware and software, and other equipment		6,649			1,758
Accumulated depreciation and amortization		(3,922	)		(1,021	)
Net other property, plant and equipment		17,563			737

Total property, plant and equipment, net	$	271,434		$	36,862

We had approximately $5.4 million and $1.9 million, at December 31, 2018 and 2017, respectively, of unproved oil and gas properties not subject to depletion. At December 31, 2018 and 2017, our unproved properties consist principally of leasehold acquisition costs in the following areas:

	As of December 31,
(in thousands)	2018		2017

Ventura Basin:
California	$	1,595	$	-
Illinois Basin:
Indiana		432		432
Illinois		136		136
Appalachian Basin:
Kentucky		920		915
Ohio		66		66
Tennessee		1,869		-
West Virginia		398		398

Total unproved properties not subject to depletion	$	5,416	$	1,947

During the year ended December 31, 2018, there were no leasehold costs reclassified into proved property.

During the year ended December 31, 2017, expiring leasehold costs reclassified into proved property were approximately $52,000. The costs not subject to depletion relate to unproved properties that are excluded from amortized capital costs until it is determined whether or not proved reserves can be assigned to such properties. These costs do not relate to any individually significant projects. The excluded properties are assessed for impairment at least annually.

We capitalized overhead applicable to acquisition and exploration activities of approximately $337,000 and $66,000 for the years ended December 31, 2018 and 2017, respectively.

Depletion expense related to oil and gas properties for the years ended December 31, 2018 and 2017 was approximately $7.3 million and $2.2 million or $0.89 and $0.40 per Mcfe, respectively. Depreciation expense related to furniture and fixtures, computer hardware and software and other equipment for the years ended December 31, 2018 and 2017 was approximately $803,000 and $387,000, respectively.