Year	constant 2021 PPP $ per kg of oil equivalent
1990	13.637063199841064
1991	13.250349768490027
1992	14.078769104319433
1993	13.992764552076155
1994	14.367806425051544
1995	14.121236774099684
1996	13.599789806229312
1997	13.986043026248407
1998	14.2455351109456
1999	14.78415080602939
2000	15.337515088280977
2001	14.698751068177172
2002	14.808315137702753
2003	14.126503850589472
2004	14.300950550266975
2005	14.245346204524484
2006	14.688934202970449
2007	15.410900911832954
2008	15.5385483296598
2009	15.833320885313878
2010	15.080751347471283
2011	15.979284217957497
2012	16.15958946929892
2013	15.936384564390838
2014	16.575481464407137
2015	16.39591710488745