[["benchmark", "2013", "2012", "2011"], ["wti crude oil ( dollars per bbl )", "$ 98.05", "$ 94.15", "$ 95.11"], ["brent ( europe ) crude oil ( dollars per bbl )", "$ 108.64", "$ 111.65", "$ 111.26"], ["henry hub natural gas ( dollars per mmbtu ) ( a )", "$ 3.65", "$ 2.79", "$ 4.04"]]