14. Segment Disclosures The Partnerships operations consist of three reportable segments: (i) Pipeline Inspection Services (Pipeline Inspection), (ii) Pipeline &amp; Process Services and (iii) Water and Environmental Services (Environmental Services). The amounts within Other represent corporate and overhead items not specifically allocable to the other reportable segments. The following table outlines segment operating income and a reconciliation of total segment operating income to net income before income tax expense. Pipeline Inspection Pipeline and Process Services Environmental Services Other Total (in thousands) Twelve months ended December 31, 2019 Revenues $ 371,994 $ 19,337 $ 10,317 $  $ 401,648 Costs of services 331,498 13,397 3,029  347,924 Gross margin 40,496 5,940 7,288  53,724 General and administrative 19,086 (a) 2,500 2,995 (b) 1,045 25,626 Depreciation, amortization and accretion 2,224 574 1,632 18 4,448 Losses (gains) on asset disposals, net 1 (26 )   (25 ) Operating income (loss) $ 19,185 $ 2,892 $ 2,661 $ (1,063 ) $ 23,675 Interest expense, net (5,330 ) Foreign currency gains 222 Other, net 1,111 Net income before income tax expense $ 19,678 Twelve months ended December 31, 2018 Revenues $ 288,083 $ 15,001 $ 11,876 $  $ 314,960 Costs of services 256,436 10,708 3,770  270,914 Gross margin 31,647 4,293 8,106  44,046 General and administrative 17,010 (c) 2,379 3,295 (b) 1,060 23,744 Depreciation, amortization and accretion 2,237 592 1,575  4,404 Gains on asset disposals, net (21 ) (83 ) (4,004 )  (4,108 ) Operating income (loss) $ 12,421 $ 1,405 $ 7,240 $ (1,060 ) $ 20,006 Interest expense, net (6,320 ) Foreign currency losses (643 ) Other, net 373 Net income before income tax expense $ 13,416 Twelve months ended December 31, 2017 Revenues $ 268,635 $ 9,268 $ 8,439 $  $ 286,342 Costs of services 241,889 7,347 3,503  252,739 Gross margin 26,746 1,921 4,936  33,603 General and administrative 13,980 (d) 1,981 2,451 (e) 2,643 (f) 21,055 Depreciation, amortization and accretion 2,331 626 1,486  4,443 Impairments 1,329 1,581 688  3,598 Losses (gains) on asset disposals, net 18  (588 )  (570 ) Operating income (loss) $ 9,088 $ (2,267 ) $ 899 $ (2,643 ) $ 5,077 Interest expense, net (7,335 ) Foreign currency gains 732 Other, net 199 Net loss before income tax expense $ (1,327 ) Total Assets December 31, 2019 $ 114,858 $ 14,318 $ 21,911 $ 6,255 $ 157,342 December 31, 2018 $ 116,239 $ 10,972 $ 24,281 $ 1,361 $ 152,853 (a) Amount includes $3.3 million of the administrative fee charged by Holdings specified in the omnibus agreement. (b) Amount includes $1.2 million of the administrative fee charged by Holdings specified in the omnibus agreement. (c) Amount includes $2.8 million of the administrative fee charged by Holdings specified in the omnibus agreement. (d) Amount includes $1.4 million of the administrative fee charged by Holdings specified in the omnibus agreement. (e) Amount includes $0.6 million of the administrative fee charged by Holdings specified in the omnibus agreement. (f) Amount includes $1.8 million of allocated general and administrative expenses incurred by Holdings but not charged to us. For the six months ended June 30, 2017, Holdings waived the administrative fee specified in the omnibus agreement.