Year	constant 2021 PPP $ per kg of oil equivalent
1990	5.833125703377762
1991	5.924783214536847
1992	6.108219264339334
1993	6.235986171982377
1994	6.373699876192709
1995	6.3126888057479755
1996	6.5403071370626975
1997	6.780474338730722
1998	6.929766948390359
1999	7.012586474668956
2000	7.225753062571525
2001	7.252186395317645
2002	7.262453934537414
2003	7.0393801917503405
2004	6.927559086992575
2005	6.926603233672543
2006	7.03546671027593
2007	7.223404639651125
2008	7.397134417767659
2009	7.342050728117144
2010	7.344560386719573
2011	7.468230547123751
2012	7.606958907833261
2013	7.773851334935105
2014	7.981423715088926