Year	constant 2021 PPP $ per kg of oil equivalent
1990	3.998042590494042
1991	4.517618304756889
1992	4.380982991296253
1993	4.691888326592008
1994	4.40299102007586
1995	4.518970252510581
1996	4.706280926590385
1997	4.304086385348676
1998	4.292826635816575
1999	4.518959319108954
2000	4.505346004889404
2001	4.493469332649307
2002	4.478764044875805
2003	4.4874626343403285
2004	4.782569850657529
2005	4.447080039073173
2006	4.419525099298436
2007	4.573966683410333
2008	4.48274461236956
2009	4.732805521152123
2010	4.776619990340826
2011	4.870055034634965
2012	5.097078332214093
2013	4.92401733690615
2014	4.972945313543568