Year	constant 2021 PPP $ per kg of oil equivalent
1990	2.145487568383781
1991	2.4070503839749926
1992	2.6590194792371675
1993	2.8587360828029786
1994	3.0853582283050653
1995	3.1883827450214275
1996	3.4099131895838286
1997	3.728811004292607
1998	3.9939543152969703
1999	4.218410592918068
2000	4.43728386068567
2001	4.619131424407342
2002	4.722630199229375
2003	4.547418944028611
2004	4.39006873285883
2005	4.423636234045834
2006	4.561033470976937
2007	4.817345086927684
2008	5.1210136625499105
2009	5.243744386061761
2010	5.252819964674905
2011	5.365333650248655
2012	5.5755967625844
2013	5.820759430696732
2014	6.157523470889378