Year	constant 2011 PPP $ per kg of oil equivalent
1990	10.3823989848857
1991	9.95652604101386
1992	9.57668958348954
1993	9.12406280877934
1994	8.72018127596571
1995	8.69973930814152
1996	8.95110938962197
1997	8.75625360322922
1998	9.09025488407182
1999	8.87387543464331
2000	9.1409032767111
2001	8.59829549927474
2002	8.40879015584073
2003	8.64138468871727
2004	8.73320049128469
2005	8.58061404952957
2006	8.52981152226584
2007	8.55091310905256
2008	8.29621052289081
2009	8.06521971749287
2010	8.09926653121856
2011	8.26773549848508
2012	7.91674199917955
2013	8.06906233898689
2014	7.85539643467875