Year	% of total fuel combustion
1971	8.333333333333332
1972	7.037037037037036
1973	5.017301038062283
1974	4.424778761061947
1975	4.844290657439446
1976	4.3383947939262475
1977	4.404873477038426
1978	4.446308724832216
1979	4.8286604361370715
1980	4.323094425483505
1981	3.909691629955947
1982	2.791878172588833
1983	2.3084479371316307
1984	2.4639702463970248
1985	2.9190207156308854
1986	2.5756891098056935
1987	4.0457343887423045
1988	3.634185303514377
1989	4.071722076951812
1990	5.071622144792877
1991	5.572876071706936
1992	5.90318772136954
1993	6.027704979408462
1994	5.784061696658098
1995	5.919854280510019
1996	6.0282665128353035
1997	6.313350709527947
1998	6.223479490806224
1999	6.867574616053318
2000	6.556039173014147
2001	6.5643197458973
2002	6.380306455664406
2003	6.239460370994941
2004	5.824098090073097
2005	5.7235923685435095
2006	3.9492580181905215
2007	4.1516245487364625
2008	4.16567483932397
2009	4.581673306772908
2010	4.412070759625391
2011	3.4332266511492584
2012	4.747908659281032
2013	3.880473127204815
2014	3.361169102296451