Year current US$ 2000 39.06169991 2001 38.05131707 2002 40.31638011 2003 48.44182713 2004 53.48508925 2005 53.71531863 2006 54.37385979 2007 59.56182384 2008 64.20702702 2009 61.05199815 2010 58.20672651 2011 54.76969646 2012 53.83768206 2013 57.41566575 2014 57.51682684 2015 48.13482084 2016 47.36023006 2017 50.20273575 2018 53.03470696 2019 51.62925116 2020 58.42785818 2021 59.01136785