In 2001, in connection with the organization of ORBCOMM Europe and the reorganization of the ORBCOMM business in Europe, the Company agreed to grant certain country representatives in Europe approximately $3,736 in airtime credits. The Company has not recorded the airtime credits as a liability for the following reasons: (i) the Company has no obligation to pay the unused airtime credits if they are not utilized; and (ii) the airtime credits are earned by the country representatives only when the Company generates revenue from the country representatives. The airtime credits have no expiration date. Accordingly, the Company is recording airtime credits as services are rendered and these airtime credits are recorded net of revenues from the country representatives. For the years ended December 31, 2018, 2017 and 2016, airtime credits used totaled approximately $30, $31, and $28, respectively. As of December 31, 2018 and 2017, unused credits granted by the Company were approximately $1,948 and $1,978, respectively.

The Company leases office, storage and other facilities under agreements classified as operating leases which expire through 2024. Future minimum lease payments, by year and in the aggregate, under non-cancelable operating leases with initial or remaining terms of one year or more as of December 31, 2018 are as follows:

Years ending December 31,
2019	$	4,161
2020		3,733
2021		3,139
2022		2,294
2023		1,960
Thereafter		3,045
	$	18,332

Rent expense for the years ended December 31, 2018, 2017 and 2016 was approximately $4,020, $3,401 and $3,047, respectively, and is recognized on a straight-line basis over the lease term.

The Company has contractual minimum payments under the terms of its agreements with certain carrier data providers. Future minimum payments, based on the number of subscribers as of December 31, 2018, for the years ending December 31, 2019, 2020, 2021 and 2022 are $7,607, $5,723, $5,866 and $6,012, respectively.

The Company has contractual minimum payments under the terms of its agreements with a vendor parts supplier. Future minimum payment for the year ended December 31, 2019 is $1,058.