Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.87960054983029
1991	3.76135551267802
1992	3.56800091058639
1993	3.01512621173911
1994	3.06558657306541
1995	3.14110130390356
1996	3.04895010086663
1997	3.53836453482452
1998	3.23412805992183
1999	2.89895089453854
2000	2.88237158649905
2001	2.8421988927658
2002	2.7193742793076
2003	2.70264498277666
2004	2.73113567504753
2005	2.71126079725594
2006	2.82704440691763
2007	2.78563093185533
2008	2.78039646664611
2009	2.41259076884865
2010	2.56006549737
2011	2.70826033263224
2012	2.89488960421578
2013	2.99151166008307
2014	3.07801267778646