bhge 2018 form 10-k | 31 business environment the following discussion and analysis summarizes the significant factors affecting our results of operations , financial condition and liquidity position as of and for the year ended december 31 , 2018 , 2017 and 2016 , and should be read in conjunction with the consolidated and combined financial statements and related notes of the company . we operate in more than 120 countries helping customers find , evaluate , drill , produce , transport and process hydrocarbon resources . our revenue is predominately generated from the sale of products and services to major , national , and independent oil and natural gas companies worldwide , and is dependent on spending by our customers for oil and natural gas exploration , field development and production . this spending is driven by a number of factors , including our customers' forecasts of future energy demand and supply , their access to resources to develop and produce oil and natural gas , their ability to fund their capital programs , the impact of new government regulations and most importantly , their expectations for oil and natural gas prices as a key driver of their cash flows . oil and natural gas prices oil and natural gas prices are summarized in the table below as averages of the daily closing prices during each of the periods indicated. .

Table:
 | 2018 | 2017 | 2016
brent oil prices ( $ /bbl ) ( 1 ) | $ 71.34 | $ 54.12 | $ 43.64
wti oil prices ( $ /bbl ) ( 2 ) | 65.23 | 50.80 | 43.29
natural gas prices ( $ /mmbtu ) ( 3 ) | 3.15 | 2.99 | 2.52
brent oil prices ( $ /bbl ) ( 1 ) $ 71.34 $ 54.12 $ 43.64 wti oil prices ( $ /bbl ) ( 2 ) 65.23 50.80 43.29 natural gas prices ( $ /mmbtu ) ( 3 ) 3.15 2.99 2.52 ( 1 ) energy information administration ( eia ) europe brent spot price per barrel ( 2 ) eia cushing , ok wti ( west texas intermediate ) spot price ( 3 ) eia henry hub natural gas spot price per million british thermal unit 2018 demonstrated the volatility of the oil and gas market .
through the first three quarters of 2018 , we experienced stability in the north american and international markets .
however , in the fourth quarter of 2018 commodity prices dropped nearly 40% ( 40 % ) resulting in increased customer uncertainty .
from an offshore standpoint , through most of 2018 , we saw multiple large offshore projects reach positive final investment decisions , and the lng market and outlook improved throughout 2018 , driven by increased demand globally .
in 2018 , the first large north american lng positive final investment decision was reached .
outside of north america , customer spending is highly driven by brent oil prices , which increased on average throughout the year .
average brent oil prices increased to $ 71.34/bbl in 2018 from $ 54.12/bbl in 2017 , and ranged from a low of $ 50.57/bbl in december 2018 , to a high of $ 86.07/bbl in october 2018 .
for the first three quarters of 2018 , brent oil prices increased sequentially .
however , in the fourth quarter , brent oil prices declined 39% ( 39 % ) versus the end of the third quarter , as a result of increased supply from the u.s. , worries of a global economic slowdown , and lower than expected production cuts .
in north america , customer spending is highly driven by wti oil prices , which similar to brent oil prices , on average increased throughout the year .
average wti oil prices increased to $ 65.23/bbl in 2018 from $ 50.80/bbl in 2017 , and ranged from a low of $ 44.48/bbl in december 2018 , to a high of $ 77.41/bbl in june 2018 .
in north america , natural gas prices , as measured by the henry hub natural gas spot price , averaged $ 3.15/ mmbtu in 2018 , representing a 6% ( 6 % ) increase over the prior year .
throughout the year , henry hub natural gas spot prices ranged from a high of $ 6.24/mmbtu in january 2018 to a low of $ 2.49/mmbtu in february 2018 .
according to the u.s .
department of energy ( doe ) , working natural gas in storage at the end of 2018 was 2705 billion cubic feet ( bcf ) , which was 15.6% ( 15.6 % ) , or 421 bcf , below the corresponding week in 2017. .

Question: what is the average percent change in natural gas prices?
Answer: 12.1%
Calculation: subtract(3.15, 2.99), divide(#0, 2.99), subtract(2.99, 2.52), divide(#2, 2.52), add(#1, #3), divide(#4, const_2)