Rental Activity

We rent natural gas compressor packages to entities in the petroleum industry. These rental arrangements are classified as operating leases and generally have original terms of six months to two years and continue on a month-to-month basis thereafter. Depreciation expense for rental equipment was $21.0 million, $19.8 million and $16.4 million for the years ended December 31, 2015, 2014 and 2013, respectively. Future minimum rent payments for arrangements not on a month-to-month basis at December 31, 2015 are as follows :



Years Ending December 31, (in thousands)
2016	$	24,284
2017	1,296
Thereafter	121
Total	$	25,701