Year	constant 2021 PPP $ per kg of oil equivalent
1990	7.701511287925304
1991	7.6265610217606215
1992	7.825066262966342
1993	7.908713201179975
1994	8.274429377377382
1995	8.3189761603276
1996	8.3088935818948
1997	8.704889629006436
1998	8.887397252527654
1999	9.153648939551767
2000	9.499925259407291
2001	9.591876677012232
2002	9.769931669735367
2003	9.744625636829083
2004	10.016363062600758
2005	10.310964850263641
2006	10.616153426192717
2007	11.148511078076048
2008	11.267578782830935
2009	11.425312072648893
2010	11.18608711366862
2011	11.583834972819398
2012	11.645911105006926
2013	11.910131216726612
2014	12.645033872028915