The following table presents the components of LNG revenues and the corresponding LNG volumes sold: Year Ended December 31, 2019 2018 2017 LNG revenues  (in millions) : LNG from the Liquefaction Projects sold under third party long-term agreements (1) $ 6,342 $ 4,762 $ 2,588 LNG from the Liquefaction Projects sold by our integrated marketing function under short-term agreements 1,943 1,902 1,756 LNG procured from third parties 268 745 981 Other revenues and derivative gains (losses) 693 163 (8) Total LNG revenues $ 9,246 $ 7,572 $ 5,317 Volumes sold as LNG revenues  (in TBtu) : LNG from the Liquefaction Projects sold under third party long-term agreements (1) 1,090 761 427 LNG from the Liquefaction Projects sold by our integrated marketing function under short-term agreements 368 212 233 LNG procured from third parties 40 84 98 Total volumes sold as LNG revenues 1,498 1,057 758 Year Ended December 31, (in millions) 2019 2018 Change 2017 Change Cost of sales $ 5,079 $ 4,597 $ 482 $ 3,120 $ 1,477 Operating and maintenance expense 1,154 613 541 446 167 Development expense 9 7 2 10 (3 ) Selling, general and administrative expense 310 289 21 256 33 Depreciation and amortization expense 794 449 345 356 93 Restructuring expense — — — 6 (6) Impairment expense and loss on disposal of assets 23 8 15 19 (11 ) Total operating costs and expenses $ 7,369 $ 5,963 $ 1,406 $ 4,213 $ 1,750 (1) Long-term agreements include agreements with a tenure of 12 months or more. Operating costs and expenses 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 61