FIXED ASSETS, NET

Fixed assets consist of the following:



	Useful Life (in years)	December 31, 2017			December 31, 2016
Equipment	7-20	$	38,843,978		$	37,260,920
Furniture and fixtures	7	108,896			108,896
Leasehold improvements	15	2,323,356			2,303,156
Office equipment	5	1,048,313			713,095
Vehicles	5	7,175,147			6,702,093
Building	20	274,203			—
Construction in progress		12,612,208			12,675,648
Land		2,851,551			2,553,000
Total fixed assets		65,237,652			62,316,808
Less accumulated depreciation		(16,617,824		)	(12,286,874		)
Net fixed assets		$	48,619,828		$	50,029,934

Depreciation expense was $4,817,264 and $4,502,597 for the years ended December 31, 2017 and 2016, respectively.

Equipment under construction in progress is related to TCEP technology improvements and refining equipment at the Marrero and Myrtle Grove facilities in Louisiana.

Asset retirement obligations:

The Company has asset retirement obligations with respect to certain of its refinery assets due to various legal obligations to clean and/or dispose of various component parts of each refinery at the time they are retired. However, these component parts can be used for extended and indeterminate periods of time as long as they are properly maintained and/or upgraded. It is the Company’s practice and current intent to maintain its refinery assets and continue making improvements to those assets based on technological advances. As a result, the Company believes that its refinery assets have indeterminate lives for purposes of estimating asset retirement obligations because dates, or ranges of dates, upon which the Company would retire refinery assets cannot reasonably be estimated. When a date or range of dates can reasonably be estimated for the retirement of any component part of a refinery, the Company estimates the cost of performing the retirement activities and records a liability for the fair value of that cost using established present value techniques.