Year	constant 2021 PPP $ per kg of oil equivalent
1990	4.878318517698562
1991	4.612353817177141
1992	4.749746892306085
1993	4.92447295838025
1994	4.834177301555556
1995	4.84773019593334
1996	5.0518524295818175
1997	5.3787674491225586
1998	5.482703059745088
1999	5.601805478515932
2000	5.874809658560779
2001	6.075362099632171
2002	6.205480745982331
2003	6.362574487717966
2004	6.779096343172882
2005	7.32957583642767
2006	7.605523689822616
2007	7.953406449987686
2008	8.159379154360147
2009	8.486945050039367
2010	8.343839605458463
2011	8.605405248888054
2012	8.89848872813353
2013	9.557074828090375
2014	10.489782927299498