Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.51980304780719
1991	3.37310059837975
1992	3.1563842751899
1993	3.05341293163398
1994	3.05251623181867
1995	3.01941578735241
1996	2.9363257977101
1997	3.11640997742127
1998	3.02160587532409
1999	3.10391300512157
2000	3.35765587912703
2001	3.49091917658215
2002	3.6720063253148
2003	3.80439986567729
2004	4.06526313385118
2005	4.29681740803917
2006	4.51767934656538
2007	4.88770822973684
2008	5.02330736297573
2009	4.92829883654994
2010	4.84037781481274
2011	4.81441536669073
2012	4.87073326314448
2013	5.03396698758979
2014	5.19710167816267