Year	% of total fuel combustion
1990	3.9070326587858166
1991	4.261511277413987
1992	4.215133018541977
1993	4.618447246184472
1994	3.5619434463365103
1995	3.5300316122233935
1996	3.321224701608718
1997	3.144870252620725
1998	3.2687866406111223
1999	3.1249999999999996
2000	4.106697370946077
2001	3.732809430255403
2002	3.6628593934619937
2003	3.698656803581856
2004	3.6907822254865956
2005	3.9265588074895477
2006	4.053817927660318
2007	4.414931801866475
2008	4.739904175222452
2009	4.113754247898409
2010	3.4580688272636153
2011	3.9170911645880913
2012	3.894080996884735
2013	4.103708791208791
2014	4.057113007139126