Year	constant 2011 PPP $ per kg of oil equivalent
1990	2.87177302264362
1991	3.38892803767302
1992	3.36284228359645
1993	3.08944632564561
1994	3.24418381612601
1995	3.07508591431405
1996	3.11385336268533
1997	3.39771209609494
1998	3.75484823551311
1999	3.7612473356548
2000	3.87879209744877
2001	3.86212903325416
2002	4.19887519205963
2003	4.30851596452382
2004	4.71465172043982
2005	4.78075886344823
2006	4.96938494906071
2007	5.42481726251223
2008	5.82971303271676
2009	6.37193363896012
2010	6.32401621917827
2011	5.98982324120323
2012	6.27531555089203
2013	6.84332041522274
2014	6.5886230485671