The most plentiful source of industrial alkenes is petrochemical cracking of petroleum oil [1]. Alkenes occur ubiquitously throughout nature, albeit in low quantities. For example, they appear in the roots of Asteraceae , in the defense system of insects such as Coleoptera, in brown algae, and in certain flowers' fragrance [2]. Alkenes have great industrial importance. The functionality of the double bond is exploited to create polymers, aldehydes, ketones, halogenated compounds, and alkanes.  In order to be used as a fuel, a conversion from alkene to alkane may be required to prevent any unwanted chemistry to occur with the double bond.  

1. olefin. (2008). In Encyclopædia Britannica. Retrieved January 22, 2008, from Encyclopædia Britannica Online: http://www.britannica.com/eb/article-9057003

2. Görgen, G., Boland, W., 1989, Eur. J. Biochem. 185, 237-242.