{"pre_text": ["natural gas prices on average were lower in 2009 than in 2008 and in 2007 , with prices in 2008 hitting uniquely high levels .", "a significant portion of our natural gas production in the lower 48 states of the u.s .", "is sold at bid-week prices or first-of-month indices relative to our specific producing areas .", "a large portion of natural gas sales in alaska are subject to term contracts .", "our other major natural gas-producing regions are europe and equatorial guinea , where large portions of our natural gas sales are also subject to term contracts , making realized prices in these areas less volatile .", "as we sell larger quantities of natural gas from these regions , to the extent that these fixed prices are lower than prevailing prices , our reported average natural gas prices realizations may be less than benchmark natural gas prices .", "oil sands mining oil sands mining segment revenues correlate with prevailing market prices for the various qualities of synthetic crude oil and vacuum gas oil we produce .", "roughly two-thirds of the normal output mix will track movements in wti and one-third will track movements in the canadian heavy sour crude oil marker , primarily western canadian select .", "output mix can be impacted by operational problems or planned unit outages at the mine or the upgrader .", "the operating cost structure of the oil sands mining operations is predominantly fixed and therefore many of the costs incurred in times of full operation continue during production downtime .", "per-unit costs are sensitive to production rates .", "key variable costs are natural gas and diesel fuel , which track commodity markets such as the canadian aeco natural gas sales index and crude prices respectively .", "the table below shows average benchmark prices that impact both our revenues and variable costs. ."], "post_text": ["western canadian select ( dollars per barrel ) ( a ) $ 52.13 $ 79.59 $ 49.60 aeco natural gas sales index ( dollars per mmbtu ) ( b ) $ 3.49 $ 7.74 $ 6.06 ( a ) monthly pricing based upon average wti adjusted for differentials unique to western canada .", "( b ) alberta energy company day ahead index .", "integrated gas our integrated gas strategy is to link stranded natural gas resources with areas where a supply gap is emerging due to declining production and growing demand .", "our integrated gas operations include marketing and transportation of products manufactured from natural gas , such as lng and methanol , primarily in west africa , the u.s .", "and europe .", "our most significant lng investment is our 60 percent ownership in a production facility in equatorial guinea , which sells lng under a long-term contract at prices tied to henry hub natural gas prices .", "in 2009 , the gross sales from the plant were 3.9 million metric tonnes , while in 2008 , its first full year of operations , the plant sold 3.4 million metric tonnes .", "industry estimates of 2009 lng trade are approximately 185 million metric tonnes .", "more lng production facilities and tankers were under construction in 2009 .", "as a result of the sharp worldwide economic downturn in 2008 , continued weak economies are expected to lower natural gas consumption in various countries ; therefore , affecting near-term demand for lng .", "long-term lng supply continues to be in demand as markets seek the benefits of clean burning natural gas .", "market prices for lng are not reported or posted .", "in general , lng delivered to the u.s .", "is tied to henry hub prices and will track with changes in u.s .", "natural gas prices , while lng sold in europe and asia is indexed to crude oil prices and will track the movement of those prices .", "we own a 45 percent interest in a methanol plant located in equatorial guinea through our investment in ampco .", "gross sales of methanol from the plant totaled 960374 metric tonnes in 2009 and 792794 metric tonnes in 2008 .", "methanol demand has a direct impact on ampco 2019s earnings .", "because global demand for methanol is rather limited , changes in the supply-demand balance can have a significant impact on sales prices .", "the 2010 chemical markets associates , inc .", "estimates world demand for methanol in 2009 was 41 million metric tonnes .", "our plant capacity is 1.1 million , or about 3 percent of total demand .", "refining , marketing and transportation rm&t segment income depends largely on our refining and wholesale marketing gross margin , refinery throughputs and retail marketing gross margins for gasoline , distillates and merchandise. ."], "table": [["benchmark", "2009", "2008", "2007"], ["wti crude oil ( dollars per barrel )", "$ 62.09", "$ 99.75", "$ 72.41"], ["western canadian select ( dollars per barrel ) ( a )", "$ 52.13", "$ 79.59", "$ 49.60"], ["aeco natural gas sales index ( dollars per mmbtu ) ( b )", "$ 3.49", "$ 7.74", "$ 6.06"]], "table_ori": [["Benchmark", "2009", "2008", "2007"], ["WTI crude oil (Dollars per barrel)", "$62.09", "$99.75", "$72.41"], ["Western Canadian Select (Dollars per barrel)<sup>(a)</sup>", "$52.13", "$79.59", "$49.60"], ["AECO natural gas sales index (Dollars per mmbtu)<sup>(b)</sup>", "$3.49", "$7.74", "$6.06"]]}

Question: what was the difference in the average price of wti crude oil and western canadian select during 2008??
Evidence:
table_1: benchmark the wti crude oil ( dollars per barrel ) of 2009 is $ 62.09 ; the wti crude oil ( dollars per barrel ) of 2008 is $ 99.75 ; the wti crude oil ( dollars per barrel ) of 2007 is $ 72.41 ;
table_2: benchmark the western canadian select ( dollars per barrel ) ( a ) of 2009 is $ 52.13 ; the western canadian select ( dollars per barrel ) ( a ) of 2008 is $ 79.59 ; the western canadian select ( dollars per barrel ) ( a ) of 2007 is $ 49.60 ;
Program: subtract(99.75, 79.59)
Answer:
str_answer: $ 20.16
exe_answer: 20.16