Year	constant 2021 PPP $ per kg of oil equivalent
1990	2.767830623652866
1991	2.8067586772554507
1992	3.0407249312928664
1993	3.2990094519476876
1994	3.4303965659442324
1995	3.322468533243755
1996	3.3259844870638857
1997	3.7145747860727596
1998	4.110495216647707
1999	4.36479480644158
2000	4.543962527691641
2001	4.738594801604023
2002	4.882666536674067
2003	5.076962377392163
2004	5.471262717718354
2005	5.991621629083938
2006	6.191717327388542
2007	6.865028236262744
2008	7.554682672388665
2009	7.972709050202139
2010	8.282831221007303
2011	8.186536529602266
2012	8.009610176318468
2013	9.045761172699748
2014	9.046051297019362