Year	constant 2021 PPP $ per kg of oil equivalent
1990	5.116467628358978
1991	4.63312602985216
1992	4.698101579322651
1993	4.573455090907311
1994	4.351054287715493
1995	4.16931856030383
1996	4.261351495664184
1997	4.337824890909
1998	4.706073451565196
1999	4.856784052997559
2000	5.090396796791995
2001	5.1994774265463946
2002	5.337644574413788
2003	5.204564156789222
2004	5.785641134204002
2005	5.939672947271246
2006	6.354889597513625
2007	6.658576270409783
2008	6.884122381049951
2009	7.0389499791873735
2010	6.926756284662256
2011	7.105891387385659
2012	7.207632041242403
2013	7.391798426059901
2014	7.58130608131549