Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.87979926207455
1991	3.99739786421545
1992	4.06256869268648
1993	4.11044003481657
1994	4.29576886255623
1995	4.30910543022043
1996	4.43213408495583
1997	4.51007285255198
1998	4.52847231174979
1999	4.48169593957781
2000	4.50858521146372
2001	4.57442492621168
2002	4.52969196638634
2003	4.57886055940591
2004	4.72517391379167
2005	4.72938295526172
2006	4.88884950802349
2007	4.9594616868774
2008	5.08435118329871
2009	5.16211273694644
2010	5.25604742122856
2011	5.25184064012716
2012	5.75689850316855
2013	5.39139186281825
2014	5.49079202063935