Year	constant 2021 PPP $ per kg of oil equivalent
1990	5.705832489016172
1991	5.509534109914048
1992	5.497213352343421
1993	5.2464207701414765
1994	5.221699422436181
1995	5.200213750415109
1996	5.307877155437835
1997	5.382641671368429
1998	5.441362824056661
1999	5.375378249689672
2000	5.527289759961841
2001	5.548674204795512
2002	5.796533684559918
2003	5.761176627803101
2004	5.902678787839116
2005	6.123390872079285
2006	6.385922241562123
2007	6.513797148150546
2008	6.4491903109755295
2009	6.605616979129444
2010	6.797321865710156
2011	6.894549098640961
2012	6.939766467152298
2013	7.141855251752747
2014	7.350387470980334