Year	constant 2021 PPP $ per kg of oil equivalent
1990	5.660446133722555
1991	5.502883474683498
1992	5.570984731017381
1993	5.393398515309177
1994	5.457725344710029
1995	5.5609355418474635
1996	5.593021577896107
1997	5.569153887276594
1998	5.527470269326409
1999	5.443267516876542
2000	5.542202470144307
2001	5.6391782001290665
2002	5.852062695248502
2003	5.977963040810797
2004	6.322234307772297
2005	6.615631273495963
2006	6.848614348266657
2007	7.025775371305676
2008	7.107130005573292
2009	7.627965883857484
2010	7.759903228306081
2011	7.748616644264899
2012	7.818008715096562
2013	8.261518231733916
2014	9.428697350714298