NOVELTY - A fuel composition comprises: isoprene; isoprene and ethanol; or isoprene and a petroleum fuel selected from gasoline, diesel, methane, ethane, butane, pentane, hexane, and heptane.    USE - As fuel composition selected from isoprene, petroleum, or ethanol fuel composition (claimed), which are useful to produce petroleum fuel blends, or with ethanol to produce biofuel. The blends of isoprene in ethanol provide replacement for ethanol in fuel blends, and are also useful in petroleum fuel blends to enhance performance of ethanol in those blends. The isoprene is useful as a direct replacement for gasoline, propane, butane, liquefied petroleum gas (LPG), or liquefied natural gas (LNG) (gas phase). The gasoline composition comprising isoprene or renewable isoprene is useful as a replacement for butane stabilizer for volatility control. The renewable isoprene fuel composition is useful in internal combustion engines or upon on-board reformation, and in fuel-cell operated engines.    ADVANTAGE - The fuel composition provides a composition containing isoprene or renewable isoprene to overcome current issues with limited oil supplies and current production of isoprene as a by-product of thermal cracking of naptha or oil, where the renewable isoprene can be combined with petroleum in varying amounts to produce fuel blend, or with ethanol to produce biofuel. This helps to reduce use of petroleum fuels; represents alternative to current reliance on petroleum fuels; helps to meet enormous need for alternatives to petroleum based fuels that do not rely on food crops; and also takes into consideration the fact that a completely re-designed engine to handle a purely bio-based or non-petroleum based fuel is unrealistic. The amount of isoprene produced by plants is far too low to collect cost efficiently. The isoprene synthesis pathway from the poplar plant has been genetically engineered to express isoprene in a variety of microorganisms including microorganisms, yeast, or fungi expressing genes that allow for expression of isoprene production components. The composition also utilizes genetically modified microalgae, cyanobacteria, and photosynthetic and non-photosynthetic bacteria in the production and harvesting of 5-carbon volatile isoprenoid compounds e.g. isoprene and methyl-butenol. Such genetically modified organisms can be used commercially in an enclosed mass culture system e.g. to provide a source of renewable fuel for internal combustion engines or upon on-board reformation, or in fuel-cell operated engines. The composition thus provides for use of isoprene, which currently is in limited supply, in petroleum fuel blend, and as replacement for ethanol in fuel blends. The composition also provides a truly renewable replacement for ethanol in fuel blends; where the current issue in use of ethanol in fuel blends has been use of food crops as a feedstock from which ethanol is derived, which has increased food prices and has had an overall detrimental effect on the world food chain.