December 31,
December 31,
December 31,
December 31,
(in thousands of $)
2019
2018
Change
% Change
Total operating revenues
218,096
127,625
90,471
71%
Vessel operating expenses
(53,689)
(26,317)
(27,372)
104%
Voyage expenses, charter-hire and commission expenses
(460)
(1,363)
903
(66)%
Administrative expenses
(1,371)
175
(1,546)
(883)%
Project development expenses
(2,939)
(16,526)
13,587
(82)%
Depreciation and amortization
(48,088)
(28,193)
(19,895)
71%
Other operating (losses)/gains
(28,963)
2,749
(31,712)
(1,154)%
Operating income
82,586
58,150
24,436
42%
Equity in net losses of affiliates
—
(2,047)
2,047
(100)%
flng segment .
total operating revenues : on may 31 2018 the hilli was accepted by the customer and accordingly commenced operations .
the hilli generated $ 218 .
1 million of total operating revenues as a result of a full year of operations during 2019 in relation to her liquefaction services compared to $ 127 .
6 million in 2018 .
vessel operating expenses : the hilli incurred $ 53 .
7 million of vessel operating expenses for the year ended december 31 2019 as a result of a full year of operations in 2019 compared to $ 26 .
3 million in 2018 following commencement of operations on may 31 2018 .
voyage charterhire and commission expenses : the decrease in voyage charterhire and commission expenses of $ 0 .
9 million to $ 0 .
5 million for the year ended december 31 2019 compared to $ 1 .
4 million in 2018 is due to lower bunker consumption as a result of the hilli undergoing commissioning in preparation for her commercial readiness in 2018 .
administrative expenses : administrative expenses increased by $ 1 .
5 million to $ 1 .
4 million for the year ended december 31 2019 compared to a credit $ 0 .
2 million in 2018 principally due to an increase in corporate expenses salaries and employee benefits following the full year of operation of the hilli compared to seven months in 2018 .
project development expenses : this relates to non-capitalized project-related expenses comprising of legal professional and consultancy costs .
the decrease was due to the commencement of capitalization of engineering consultation fees in relation to the gimi gta project following the gimi entering keppel ' s shipyard for her conversion into a flng in december 2018 .
depreciation and amortization : following the hilli ' s commencement of operations on may 31 2018 depreciation and amortization of the vessel was recognized .
a full year of depreciation was recognized for the year ended december 31 2019 compared to the seven months of depreciation in 2018 .
other operating -losses / gains : included in other operating -losses / gains are : • realized gain on the oil derivative instrument based on monthly billings above the base tolling fee under the lta of $ 13 .
1 million for the year ended december 31 2019 compared to $ 26 .
7 million in 2018 ; • unrealized loss on the oil derivative instrument due to changes in oil prices above a contractual floor price over term of the lta of $ 39 .
1 million for the year ended december 31 2019 compared to unrealized loss of $ 10 .
0 million in 2018 ; and • write-off of $ 3 .
0 million and $ 12 .
7 million of unrecoverable receivables relating to onelng for the year ended december 31 2019 and 2018 respectively .
equity in net losses of affiliates : in april 2018 we and schlumberger decided to wind down onelng and work on flng projects on a case-by-case basis .

Question: What are the different components of expenses?
Answer: Vessel operating expenses Voyage expenses, charter-hire and commission expenses Administrative expenses Project development expenses Depreciation and amortization Other operating (losses)/gains