Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.66629459640296
1991	4.7025270563197
1992	4.81745480925814
1993	4.91776917807963
1994	5.0810948839167
1995	5.11005328746164
1996	5.27660729759417
1997	5.47061468143105
1998	5.57274434448522
1999	5.66063419138289
2000	5.84485017577012
2001	5.91702609231011
2002	5.98155551091781
2003	5.94379703065605
2004	5.98416724473539
2005	6.0843880016489
2006	6.22938519055766
2007	6.44902643526992
2008	6.58402543390025
2009	6.60802735330654
2010	6.62517715104753
2011	6.7065696534793
2012	6.81566595220925
2013	7.03009944246427
2014	7.24870495590548