Vegetable oils are increasingly used as a substitute for fossil fuels. Vegetable oils are the basis of biodiesel, which can be used like conventional diesel. Some vegetable oil blends are used in unmodified vehicles, but straight vegetable oil often needs specially prepared vehicles which have a method of heating the oil to reduce its viscosity and surface tension, sometimes specially made injector nozzles, increased injection pressure and stronger glow-plugs, in addition to fuel pre-heating is used. Another alternative is vegetable oil refining. The availability of biodiesel around the world is increasing, although still tiny compared to conventional fossil fuel sources. There is significant research in algaculture methods to make biofuel from algae. Concerns have been expressed about growing crops for fuel use rather than food and the environmental impacts of large-scale agriculture and land clearing required to expand the production of vegetable oil for fuel use. These effects/impacts would need to be specifically researched and evaluated, economically and ecologically, and weighed in balance with the proposed benefits of vegetable oil fuel in relation to the use of other fuel sources. Future of energy for world economy There is a limited amount of fossil fuel inside the Earth. Since the current world energy resources and consumption is mainly fossil fuels, society is very dependent on them for both transportation and electric power generation. The Hubbert peak theory predicts that oil depletion will result in oil production dropping off in the not too distant future. As time goes on our economy will have to transition to some alternative fuels. Fossil fuels have solved two problems which could be separately solved in the future: the problem of a source of primary energy and of energy storage. Along with straight vegetable oil and biodiesel, some energy technologies that could play an important part in the future include: | width="30%" align="left" valign="top" style="border:0"| hydrogen economy methanol fuel ethanol fuel lithium economy zinc-air battery liquid nitrogen economy synthetic fuel | width="30%" align="left" valign="top" style="border:0"| solar energy / photovoltaics nuclear power (fission power) fusion power wind power compressed air energy storage flywheel energy storage biofuel | width="30%" align="left" valign="top" style="border:0"| Net CO2 or greenhouse gas production Plants use sunlight and photosynthesis to take carbon dioxide (CO2) out of the Earth's atmosphere to make vegetable oil. The same CO2 is then put back after it is burned in an engine. Thus vegetable oil does not increase the CO2