Year	constant 2011 PPP $ per kg of oil equivalent
1990	5.94628171749889
1991	5.84098422162258
1992	5.9402202968617
1993	6.02540974207588
1994	6.15623506253001
1995	6.23265197707691
1996	6.44390001598521
1997	6.4380525301485
1998	6.63381228876323
1999	6.7672144881777
2000	6.86442149746178
2001	7.0404620683826
2002	7.10895954007887
2003	7.41276863111614
2004	7.580037997809
2005	7.86185684086283
2006	8.05996510653457
2007	8.19427754907928
2008	8.12280326754551
2009	7.99036834775196
2010	8.23229724495606
2011	8.3283128198525
2012	8.40132419887762
2013	8.71458146799406
2014	8.81896706604384