( 2 ) our union-represented mainline employees are covered by agreements that are not currently amendable . joint collective bargaining agreements ( jcbas ) have been reached with post-merger employee groups , except the maintenance , fleet service , stock clerks , maintenance control technicians and maintenance training instructors represented by the twu-iam association who are covered by separate cbas that become amendable in the third quarter of 2018 . until those agreements become amendable , negotiations for jcbas will be conducted outside the traditional rla bargaining process as described above , and , in the meantime , no self-help will be permissible . ( 3 ) among our wholly-owned regional subsidiaries , the psa mechanics and flight attendants have agreements that are now amendable and are engaged in traditional rla negotiations . the envoy passenger service employees are engaged in traditional rla negotiations for an initial cba . the piedmont fleet and passenger service employees have reached a tentative five-year agreement which is subject to membership ratification . for more discussion , see part i , item 1a . risk factors 2013 201cunion disputes , employee strikes and other labor-related disruptions may adversely affect our operations . 201d aircraft fuel our operations and financial results are significantly affected by the availability and price of jet fuel , which is our second largest expense . based on our 2018 forecasted mainline and regional fuel consumption , we estimate that a one cent per gallon increase in aviation fuel price would increase our 2018 annual fuel expense by $ 45 million . the following table shows annual aircraft fuel consumption and costs , including taxes , for our mainline and regional operations for 2017 , 2016 and 2015 ( gallons and aircraft fuel expense in millions ) . year gallons average price per gallon aircraft fuel expense percent of total operating expenses .

gallons: 2017: 4352
2016: 4347
2015: 4323
average priceper gallon: 2017: 1.73
2016: 1.42
2015: 1.72
aircraft fuelexpense: 2017: 7510
2016: 6180
2015: 7456
percent of totaloperating expenses: 2017: -19.7
2016: -17.7
2015: -21.4

as of december 31 , 2017 , we did not have any fuel hedging contracts outstanding to hedge our fuel consumption . as such , and assuming we do not enter into any future transactions to hedge our fuel consumption , we will continue to be fully exposed to fluctuations in fuel prices . our current policy is not to enter into transactions to hedge our fuel consumption , although we review that policy from time to time based on market conditions and other factors . fuel prices have fluctuated substantially over the past several years . we cannot predict the future availability , price volatility or cost of aircraft fuel . natural disasters ( including hurricanes or similar events in the u.s . southeast and on the gulf coast where a significant portion of domestic refining capacity is located ) , political disruptions or wars involving oil-producing countries , changes in fuel-related governmental policy , the strength of the u.s . dollar against foreign currencies , changes in access to petroleum product pipelines and terminals , speculation in the energy futures markets , changes in aircraft fuel production capacity , environmental concerns and other unpredictable events may result in fuel supply shortages , distribution challenges , additional fuel price volatility and cost increases in the future . see part i , item 1a . risk factors 2013 201cour business is very dependent on the price and availability of aircraft fuel . continued periods of high volatility in fuel costs , increased fuel prices or significant disruptions in the supply of aircraft fuel could have a significant negative impact on our operating results and liquidity . 201d seasonality and other factors due to the greater demand for air travel during the summer months , revenues in the airline industry in the second and third quarters of the year tend to be greater than revenues in the first and fourth quarters of the year . general economic conditions , fears of terrorism or war , fare initiatives , fluctuations in fuel prices , labor actions , weather , natural disasters , outbreaks of disease and other factors could impact this seasonal pattern . therefore , our quarterly results of operations are not necessarily indicative of operating results for the entire year , and historical operating results in a quarterly or annual period are not necessarily indicative of future operating results. .

Questions:
what was the aircraft fuel expense in 2016?
and in 2017?
so what was the combined value during these years?
and the value for 2015?
so for all three years, what was the total value?

Answers:
6180
7510
13690
7456
21146