Year	constant 2011 PPP $ per kg of oil equivalent
1990	6.61352926308558
1991	6.19142890405264
1992	6.30316329504317
1993	6.18424411307347
1994	6.26175856711183
1995	6.04418122147505
1996	6.00309120239476
1997	6.07009825516009
1998	6.39251008729293
1999	6.74835141905418
2000	7.04734881057667
2001	6.9079951853905
2002	7.07345278970216
2003	7.18808716199389
2004	7.27009012086656
2005	7.39349364157279
2006	7.78006886716382
2007	8.31113027319944
2008	8.11593587066263
2009	8.13777963814634
2010	8.01279463895026
2011	8.07310495232435
2012	8.17073256281153
2013	8.29263519799169
2014	8.77864136055691
2015	9.1476821372893