Year	constant 2021 PPP $ per kg of oil equivalent
1990	7.063936190706643
1991	7.136384281531247
1992	7.035589353056483
1993	6.9837224836557565
1994	7.266715963536848
1995	7.400910165674551
1996	7.21470401219556
1997	7.310586824778836
1998	7.457562108269925
1999	7.665278015239632
2000	7.824434557604551
2001	8.160955793068739
2002	8.198162166948368
2003	8.349204061883368
2004	8.556542313458028
2005	8.763931985467597
2006	8.647768447957125
2007	8.676560360034218
2008	8.667142464403788
2009	8.801706275667774
2010	8.964985606018475
2011	9.129723051506454
2012	9.607456891745802
2013	9.879041793800345
2014	10.236860809158376
2015	10.032300947070256