Related by context. Frequent words. (Click for all words.) 70 fossil fuels 67 fossil fuel 54 alternative fuels 53 biofuels 52 fuels 52 bio fuels 51 alternative energies 51 renewable energy 51 liquid fuels 50 biofuel 50 polluting 50 energy 49 renewable fuels 49 cleaner burning 49 ethanol 49 renewable 48 coal 48 fuel 47 renewable energies 47 diesel 47 hydrogen 47 internal combustion engines 46 internal combustion engine 46 polluting industries 46 burning fossil fuels 46 renewables 46 greenhouse gasses 45 carbon 45 biomass 44 gas guzzlers 44 biodiesel 44 gas guzzling 44 Renewable energy 43 bio diesel 43 greenhouse gases 43 incandescent bulbs 43 hydroelectricity 43 gasoline 43 combustion engine 42 Biofuel 42 synthetic fuels 42 environmentally friendly 42 cellulosic ethanol 42 feedstock 42 natural gas 42 coal fired 42 carbon emissions 42 diesel fuel 41 carbon emission 41 hydrogen fuel 41 petroleum 41 coal gasification 41 Ethanol 41 electricity 41 hydrogen powered 41 pollute 40 wean itself 40 feedstocks 40 combustion 40 syngas 40 reducing carbon emissions 40 chemical fertilizers 40 environmentally sound 40 carbon dioxide emissions 40 carbon dioxide 40 reduce carbon emissions 40 carbon credits 40 Hydrogen 40 greenhouse emissions 40 greenhouse gas emissions 40 diesels 40 baseload 40 greenhouse gas 40 biogas 39 tar sands 39 ecologically friendly 39 diesel engines 39 CO2 39 exhaust emissions 39 wood stoves 39 bioethanol 39 diesel powered 39 carbon capture 38 thorium 38 environmentally sustainable 38 cleaner 38 vegetable oils 38 emissions 38 HFCs 38 environmentally 38 compressed natural 38 incandescent light 38 carbon offsets 38 methanol 38 reduce greenhouse gas 38 emission 38 CO2 emissions 38 FutureGen 38 oil 38 rare earths 37 zero emission