Year	constant 2021 PPP $ per kg of oil equivalent
1990	7.220252986752865
1991	7.126917382265868
1992	7.205308831795232
1993	7.216960390896906
1994	7.384942353719286
1995	7.479202928340546
1996	7.683196230298594
1997	7.714418089532243
1998	7.835249827549382
1999	7.943777930730119
2000	8.135209500353119
2001	8.312375695735744
2002	8.405413059184328
2003	8.687976170620532
2004	8.878537528640916
2005	9.141016948790442
2006	9.420403342071472
2007	9.644599549152305
2008	9.689501669803393
2009	9.753915711969272
2010	10.003907499120945
2011	10.064051599931254
2012	10.119996715724476
2013	10.555073604080635
2014	10.891168152736496