Year	% of total fuel combustion
1971	26.666666666666668
1972	22
1973	19.76744186046512
1974	20.21857923497268
1975	20
1976	18.560606060606062
1977	17.857142857142858
1978	16.666666666666668
1979	17.052023121387283
1980	16.937354988399072
1981	15.779467680608365
1982	15.191986644407345
1983	13.169984686064318
1984	12.85310734463277
1985	11.512717536813923
1986	9.344660194174757
1987	8.870967741935484
1988	10.225921521997622
1989	10.928319623971799
1990	11.29032258064516
1991	10.932475884244374
1992	12.906220984215414
1993	11.8348623853211
1994	14.47140381282496
1995	11.092985318107667
1996	15.968379446640316
1997	16.465256797583084
1998	14.919941775836973
1999	15.69767441860465
2000	16.701316701316703
2001	15.874125874125875
2002	15.019762845849804
2003	16.744496330887255
2004	16.092636579572446
2005	15.626725565985645
2006	14.324324324324325
2007	12.674599068804968
2008	10.88471849865952
2009	11.019567456230691
2010	9.639830508474576
2011	9.934771700953336
2012	8.252853380158033
2013	6.812110418521816
2014	6.553297386976359