Year	constant 2021 PPP $ per kg of oil equivalent
1990	5.045482127452488
1991	4.831802440861249
1992	4.721911558631395
1993	4.7035807036311486
1994	4.75800336077609
1995	4.76288151128946
1996	4.7942846703096675
1997	5.0799570592216385
1998	5.127345967683343
1999	5.269231577621646
2000	5.60850912603431
2001	5.788722122239189
2002	6.016587136520057
2003	6.173713559594388
2004	6.59396685890384
2005	6.990534101750148
2006	7.288491162899648
2007	7.78045367336073
2008	8.016730964455927
2009	8.135509629129762
2010	7.959307533716381
2011	8.051774546196004
2012	8.242345395182582
2013	8.632782358011502
2014	9.115214017399527