Year	% of total fuel combustion
1971	15.384615384615385
1972	13.793103448275865
1973	18.18181818181818
1974	15
1975	14.285714285714285
1976	14.285714285714288
1977	14.285714285714285
1978	15
1979	14.754098360655737
1980	12.280701754385968
1981	10.344827586206897
1982	9.433962264150944
1983	9.836065573770492
1984	9.23076923076923
1985	9.836065573770492
1986	9.210526315789474
1987	11.11111111111111
1988	10
1989	9.900990099009901
1990	10.344827586206897
1991	9.6
1992	9.848484848484848
1993	8.843537414965986
1994	7.9470198675496695
1995	8.38709677419355
1996	8.074534161490684
1997	8.024691358024691
1998	7.82122905027933
1999	6.363636363636364
2000	6.17283950617284
2001	5.859375000000001
2002	5.747126436781611
2003	6.181818181818182
2004	6.4981949458483745
2005	6.081081081081081
2006	5.151515151515152
2007	4.71976401179941
2008	4.610951008645533
2009	4.678362573099416
2010	4.644808743169399
2011	4.670329670329671
2012	4.557640750670242
2013	4.699738903394256
2014	4.545454545454546