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The following table presents the components of LNG revenues and the corresponding LNG volumes sold: 

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(1) Long-term agreements include agreements with a tenure of 12 months or more. 

## Operating costs and expenses 

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## 2019 vs. 2018 and 2018 vs. 2017 

Our total operating costs and expenses increased during the year ended December 31, 2019 from the years ended December 31, 2018 and 2017, primarily as a result of the increase in operating Trains between each of the periods. During the year ended December 31, 2019, we further incurred increased third-party service and maintenance costs from turnaround and related activities at the SPL Project. 

Cost of sales includes costs incurred directly for the production and delivery of LNG from the Liquefaction Projects, to the extent those costs are not utilized for the commissioning process. Cost of sales increased during the year ended December 31, 2019 from the comparable 2018 and 2017 periods, primarily as a result of the increase in operating Trains between each of the periods. Cost of sales increased during the year ended December 31, 2019 from the year ended December 31, 2018 due to increased volume of natural gas feedstock partially offset by its decreased pricing and increased vessel charter costs. Partially offsetting this increase was increased derivative gains from an increase in fair value of the derivatives associated with economic hedges to secure natural gas feedstock for the Liquefaction Projects, primarily due to a favorable shift in long- term forward prices. Cost of sales also includes port and canal fees, variable transportation and storage costs and the sale of natural gas procured for the liquefaction process and other costs to convert natural gas into LNG. The increase during the year ended December 31, 2018 from the comparable period in 2017 was primarily related to the increase in the volume of natural gas feedstock related to our LNG sales. 

Operating and maintenance expense primarily includes costs associated with operating and maintaining the Liquefaction Projects. The increase in operating and maintenance expense during the year ended December 31, 2019 from the comparable 2018 and 2017 periods was primarily as a result of the increase in operating Trains between each of the periods. The increase during the year ended December 31, 2019 from the comparable period in 2018 was primarily related to: (1) increased natural gas transportation and storage capacity demand charges from operating Train 5 of the SPL Project and Trains 1 and 2 of the CCL 

