Year	constant 2011 PPP $ per kg of oil equivalent
1990	1.87366842928536
1991	1.90002057218681
1992	2.05840279887471
1993	2.23324715225064
1994	2.32218896859384
1995	2.24912765368889
1996	2.25150776069399
1997	2.51456192507566
1998	2.78257818662732
1999	2.95472495847516
2000	3.07601161025674
2001	3.20776690595465
2002	3.3052955108258
2003	3.43682306295558
2004	3.70374261263077
2005	4.05599684718756
2006	4.19145058450737
2007	4.64724487173057
2008	5.11410282492189
2009	5.39708359288353
2010	5.60701916987494
2011	5.54183298051221
2012	5.42206361341831
2013	6.12348060194222
2014	6.12368752652451