[["year", "gallons consumed ( in millions )", "average costper gallon", "total cost ( in millions )", "percent of total operating expenses"], ["2011", "2756", "$ 3.01", "$ 8304", "33.2% ( 33.2 % )"], ["2012", "2723", "$ 3.20", "$ 8717", "35.3% ( 35.3 % )"], ["2013", "2806", "$ 3.09", "$ 8959", "35.3% ( 35.3 % )"]]