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.
Table:
 |  | 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)%


Question: What was the percentage change in operating income?
Answer: 42.02
Calculation: (82,586 - 58,150)/58,150