{"pre_text": ["our international crude oil production is relatively sweet and is generally sold in relation to the brent crude benchmark .", "the differential between wti and brent average prices widened significantly in 2011 and remained in 2012 in comparison to almost no differential in 2010 .", "natural gas 2013 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 .", "average henry hub settlement prices for natural gas were lower in 2012 than in recent years .", "a decline in average settlement date henry hub natural gas prices began in september 2011 and continued into 2012 .", "although prices stabilized in late 2012 , they have not increased appreciably .", "our other major natural gas-producing regions are e.g .", "and europe .", "in the case of e.g .", "our natural gas sales are subject to term contracts , making realizations less volatile .", "because natural gas sales from e.g .", "are at fixed prices , our worldwide reported average natural gas realizations may not fully track market price movements .", "natural gas prices in europe have been significantly higher than in the u.s .", "oil sands mining the osm segment produces and sells various qualities of synthetic crude oil .", "output mix can be impacted by operational problems or planned unit outages at the mines or upgrader .", "sales prices for 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 wcs .", "in 2012 , the wcs discount from wti had increased , putting downward pressure on our average realizations .", "the operating cost structure of the osm 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 alberta energy company ( \"aeco\" ) natural gas sales index and crude oil prices , respectively .", "the table below shows average benchmark prices that impact both our revenues and variable costs. ."], "post_text": ["wcs ( dollars per bbl ) ( a ) $ 73.18 $ 77.97 $ 65.31 aeco natural gas sales index ( dollars per mmbtu ) ( b ) $ 2.39 $ 3.68 $ 3.89 ( a ) monthly pricing based upon average wti adjusted for differentials unique to western canada .", "( b ) monthly average day ahead index .", "integrated gas our ig operations include production and marketing of products manufactured from natural gas , such as lng and methanol , in e.g .", "world lng trade in 2012 has been estimated to be 240 mmt .", "long-term , lng 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 have a 60 percent ownership in an lng production facility in e.g. , which sells lng under a long-term contract at prices tied to henry hub natural gas prices .", "gross sales from the plant were 3.8 mmt , 4.1 mmt and 3.7 mmt in 2012 , 2011 and 2010 .", "we own a 45 percent interest in a methanol plant located in e.g .", "through our investment in ampco .", "gross sales of methanol from the plant totaled 1.1 mmt , 1.0 mmt and 0.9 mmt in 2012 , 2011 and 2010 .", "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 .", "world demand for methanol in 2012 has been estimated to be 49 mmt .", "our plant capacity of 1.1 mmt is about 2 percent of world demand. ."], "table": [["benchmark", "2012", "2011", "2010"], ["wti crude oil ( dollars per bbl )", "$ 94.15", "$ 95.11", "$ 79.61"], ["wcs ( dollars per bbl ) ( a )", "$ 73.18", "$ 77.97", "$ 65.31"], ["aeco natural gas sales index ( dollars per mmbtu ) ( b )", "$ 2.39", "$ 3.68", "$ 3.89"]], "table_ori": [["Benchmark", "2012", "2011", "2010"], ["WTI crude oil(Dollars per bbl)", "$94.15", "$95.11", "$79.61"], ["WCS(Dollars per bbl)<sup>(a)</sup>", "$73.18", "$77.97", "$65.31"], ["AECO natural gas sales index(Dollars per mmbtu)<sup>(b)</sup>", "$2.39", "$3.68", "$3.89"]]}

Question: what was the difference in the average price of wti crude and wcs in 2012?
Evidence:
table_1: benchmark the wti crude oil ( dollars per bbl ) of 2012 is $ 94.15 ; the wti crude oil ( dollars per bbl ) of 2011 is $ 95.11 ; the wti crude oil ( dollars per bbl ) of 2010 is $ 79.61 ;
table_2: benchmark the wcs ( dollars per bbl ) ( a ) of 2012 is $ 73.18 ; the wcs ( dollars per bbl ) ( a ) of 2011 is $ 77.97 ; the wcs ( dollars per bbl ) ( a ) of 2010 is $ 65.31 ;
Program: subtract(94.15, 73.18)
Answer:
str_answer: $ 20.97
exe_answer: 20.97