4. Property, Plant and Equipment

Property, plant and equipment was comprised of the following at September 30, 2017 and December 31, 2016:


	September 30,		December 31,
	2017		2016
Proppant management systems and related equipment	$	89,011	$	51,899
Machinery and equipment		4,269		3,916
Furniture and fixtures		78		7
Computer equipment		1,552		829
Vehicles		3,323		1,235
Buildings		3,237		3,008
Logistics systems in process		4,793		—
Proppant management systems in process		5,999		1,252
Land		578		578
Property, plant and equipment, gross		112,840		62,724
Less: accumulated depreciation		(12,834)		(8,374)
Property, plant and equipment, net	$	100,006	$	54,350

Depreciation expense for the three months ended September 30, 2017 and 2016 was $1,742 and $959, respectively, of which $1,523 and $857 is attributable to cost of proppant management system rental, $129 and $42 is attributable to cost of proppant management system services, and $90 and $60 is attributable to selling, general and administrative expenses, respectively. Depreciation expense for the nine months ended September 30, 2017 and 2016 was $4,276 and $2,739, respectively, of which $3,748 and $2,418 is attributable to cost of proppant management system rental, $283 and $111 is attributable to cost of proppant management system services, and $245 and $210 is attributable to selling, general and administrative expenses, respectively. The Company capitalized $172 and $173 of depreciation expense associated with machinery and equipment used in the manufacturing of its systems for the three months ended as of September 30, 2017 and 2016, respectively. The Company capitalized $492 and $515 of depreciation expense associated with machinery and equipment used in the manufacturing of its systems for the nine months ended as of September 30, 2017 and 2016, respectively.

In July 2017, the company acquired a lease for $250 in connection with the Kingfisher Facility described in Note 12. Refer to Note 12 for commitments and contingencies in connection with additional construction plans for this asset. This asset as well as construction costs incurred through September 30, 2017 are recognized in property, plant and equipment as Logistics systems in process.