COMMITMENTS AND CONTINGENCIES Contingencies We have contingent liabilities resulting from various litigation, claims and commitments. We record accruals for loss contingencies when losses are considered probable and can be reasonably estimated. Legal fees associated with defending the Partnership in legal matters are expensed as incurred. We accrued $2.8 million and $7.3 million for contingent losses as of December 31, 2018 and 2017 , respectively. The amount that will ultimately be paid related to such matters may differ from the recorded accruals, and the timing of such payments is uncertain. We evaluate each contingent loss at least quarterly, and more frequently as each matter progresses and develops over time, and we do not believe that the resolution of any particular claim or proceeding, or all matters in the aggregate, would have a material adverse effect on our results of operations, financial position or liquidity. Commitments Lessee and Other Commitments. Future minimum rental payments applicable to all noncancellable operating leases and purchase obligations as of December 31, 2018 are as follows: Payments Due by Period 2019 2020 2021 2022 2023 There- after Total (Thousands of Dollars) Operating leases $ 34,900 $ 20,787 $ 14,904 $ 9,280 $ 6,870 $ 28,552 $ 115,293 Purchase obligations $ 10,896 $ 7,958 $ 7,011 $ 4,970 $ 602 $ 2,624 $ 34,061 Rental expense for operating leases totaled $42.9 million , $36.2 million and $37.0 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Our operating leases consist primarily of the following:  two leases for tugs and barges utilized at our St. Eustatius facility for bunker fuel sales, with original terms of nine and ten years ; and  land and dock leases at various terminal facilities, with original terms generally ranging from 5 to 40 years, including a build-to-suit lease with an initial term of five years and four additional five-year renewal periods that also includes a commitment for minimum dockage and wharfage throughput volumes. Our purchase obligations primarily consist of an eleven-year chemical supply agreement related to our pipelines. Lessor Revenues. We have entered into certain revenue arrangements where we are considered to be the lessor in accordance with GAAP. Under these arrangements, we lease certain of our storage tanks in exchange for a fixed fee, subject to an annual consumer price index adjustment. The arrangements commenced on January 1, 2017, and have initial terms of ten years with successive ten -year automatic renewal terms. We recognized $39.8 million of lease revenues from these leases for the year ended December 31, 2018 , which is included in Service revenues in the consolidated statements of income. Future minimum revenues we expect to receive under these lease arrangements as of December 31, 2018 total $313.1 million , which we will recognize ratably over the following eight years. As of December 31, 2018 , the cost and accumulated depreciation of leased storage assets totaled $233.2 million and $113.1 million , respectively.