Year	% of total fuel combustion
1971	4.282159100660775
1972	4.201455791051167
1973	4.087516960651289
1974	4.223045960020922
1975	4.399681950702359
1976	4.322439547742841
1977	4.110316087435131
1978	3.9986763002592247
1979	4.255838271174625
1980	4.334797905829672
1981	4.059775423799722
1982	4.208684744755648
1983	4.120523635874772
1984	4.078122674428219
1985	4.5567064034916305
1986	4.078965790824659
1987	4.357493545835759
1988	4.428569333000836
1989	4.201163971229605
1990	3.8782130544200872
1991	3.6593059936908516
1992	3.7327201630225257
1993	3.8687396696991287
1994	4.189866369710468
1995	3.9950806842321023
1996	4.051004818427548
1997	4.025367451744288
1998	3.5024154589371985
1999	3.7082726276945333
2000	3.528456110067523
2001	3.701101675932147
2002	3.6147274206672093
2003	3.805872545202224
2004	3.9747003994673773
2005	3.9563311492729576
2006	3.8143754612712186
2007	3.714739942141797
2008	4.158348841143631
2009	4.364043267437523
2010	4.021611081772759
2011	3.731639539499802
2012	3.8771653780424455
2013	3.7507119030184684
2014	4.034744434897507