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
table: WTI crude oil(Dollars per bbl) $94.15 $95.11 $79.61
table: WCS(Dollars per bbl)<sup>(a)</sup> $73.18 $77.97 $65.31
table: AECO natural gas sales index(Dollars per mmbtu)<sup>(b)</sup> $2.39 $3.68 $3.89
question: Analyse this data from a financial earnings document. what was the difference in the average price of wti crude and wcs in 2012?