NOTE H — LEASE RENTAL REVENUES AND AIRCRAFT AND ENGINES HELD FOR LEASE

Aircraft and engines held for operating leases, net, as of the below dates consisted of the following (in thousands):

​

​

Total depreciation expense amounted to $2.2 million and $5.4 million for the three months ended June 30, 2021 and 2020, respectively. Total depreciation expense amounted to $4.6 million and $12.5 million for the six months ended June 30, 2021 and 2020, respectively, and is included in cost of leasing in the condensed consolidated statements of operations.

Supplemental rents recognized as revenue totaled $1.8 million and $2.1 million for the three months ended June 30, 2021 and 2020, respectively. Supplemental rents recognized as revenue totaled $2.9 million and $7.6 million for the six months ended June 30, 2021 and 2020, respectively.

The Company’s current operating lease agreements for flight equipment on lease expire over the next month to three years. The amounts in the following table are based upon the assumption that flight equipment under operating leases will remain on lease for the length of time specified by the respective lease agreements. Minimum future annual lease rentals contracted to be received under existing operating leases of flight equipment at were as follows (in thousands):

​

​