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. .
by what percentage did the average price of the wti crude oil benchmark decrease from 2008 to 2009?
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. .