Year	constant 2021 PPP $ per kg of oil equivalent
1990	7.011102942341259
1991	7.017219472793969
1992	7.104837853059247
1993	7.1232818175198105
1994	7.2719791449137645
1995	7.298651577178784
1996	7.380582190716832
1997	7.596361011333952
1998	7.754838582236619
1999	7.865534483551942
2000	8.058425712807514
2001	8.15391871495448
2002	8.210332905276088
2003	8.21020383361966
2004	8.265879019146292
2005	8.406777147223055
2006	8.59696316909818
2007	8.796295165094275
2008	8.921901167968208
2009	8.91392371965264
2010	8.875973271105353
2011	9.077721704835373
2012	9.193176537655072
2013	9.365035643852515
2014	9.592914418181136