( 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 .

Year
Gallons
Average Priceper Gallon
Aircraft FuelExpense
Percent of TotalOperating Expenses
2017
4,352
$1.73
$7,510
19.7%
2016
4,347
1.42
6,180
17.7%
2015
4,323
1.72
7,456
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. .

Question: Analyse this data from a financial earnings document. what is the percentage change in the average price per gallon of aircraft fuel from 2016 to 2017?
Choices:
0.21831
0.4402
-0.21831
0.17919
0.18023
Correct choice index: 0