In the year 2000, there were about eight million vehicles around the world that ran on alternative fuels, indicating the increasing popularity of alternative fuels. There is growing social interest, and an economic and political need for the development of alternative fuel sources. This is due to general concerns of sustainability, both environmental, economic, and geopolitical. A primary concern is that the fact that the use of conventional fuels directly contributes to the global warming crisis. Another concern is the problem of peak oil, which predicts a rising cost of oil derived fuels caused by severe shortages of oil during an era of growing energy consumption. According to the 'peak oil' phenomenon, the demand for oil will exceed supply and this gap will continue to grow, which could cause a growing energy crisis by the year 2010 or 2020. Lastly, the majority of the known petroleum reserves are located in the middle east. There is general concern that worldwide fuel shortages could intensify the unrest that exists in the region, leading to further conflict and war.