Year	constant 2021 PPP $ per kg of oil equivalent
1990	6.879534623146199
1991	6.38189209572311
1992	6.549673270342605
1993	6.202618372442478
1994	6.03869413871514
1995	6.6133446005865455
1996	6.373770369213933
1997	6.534785180173566
1998	6.827041167216022
1999	7.149529966994445
2000	7.572845293703113
2001	7.573314903730708
2002	7.320853666525991
2003	7.082964796162784
2004	7.284842175438149
2005	8.11314360277677
2006	7.757556058142631
2007	8.293696904080324
2008	8.70129018763919
2009	8.4696428762138
2010	7.985558207685111
2011	8.51413206851783
2012	8.703930815067896
2013	8.809762932121119
2014	8.604739630109295
2015	9.043195338143544