Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.8911284875221
1991	3.89197165021554
1992	3.86481277360716
1993	3.80813939515929
1994	3.79950450458485
1995	3.75579189140125
1996	3.87848809289134
1997	3.97691922875027
1998	3.87316982024841
1999	3.82058354749014
2000	3.78305304278686
2001	3.79975698161144
2002	3.87274442629289
2003	3.97419711195283
2004	4.02887753069455
2005	4.13509399820107
2006	4.2521436335408
2007	4.38486537997699
2008	4.48289118342143
2009	4.5901431206406
2010	4.64351264307892
2011	4.72961059556662
2012	4.65704807110436
2013	4.79930464885929
2014	4.95444877261591