In recent years, fuel ethanol production has been revived for use in gasoline trans­port fuel markets. The main driver for fuel ethanol expansion use has been the need for a gasoline oxygenate, following the issues that were uncovered concern­ing the previous widespread petroleum industry oxygenate, methyl tert-butyl ether (MTBE). Ethanol is biologically safer, biodegradeable, renewable, and carries 88% more oxygen than MTBE (especially useful in the higher compression modern gaso­line engines). A secondary, but nonetheless important, driver for ethanol expansion has been to reduce dependence on foreign oil for those countries that import large volumes of crude oil. The success of ethanol to-date has relied on the harvested por­tions of mainstream agricultural crops, where modern-technology yield increases have allowed increasing harvest volumes [17].

The global production of crop-based renewable ethanol is projected at around 20 billion gallons (77 B liters) for 2008. Figure 1 shows the breakdown by country and main feedstock. In Brazil, fuel ethanol displaces ~20-50% of the transporta­tion petroleum gasoline, with the volume depending on the world price of sugar. Projections are for additional areas to be planted with sugarcane to meet the demand for sugar and fuel, and there are plans to utilize more biotechnology to increase

sugarcane yields by over 10% [2]. The fuel ethanol industry in the USA has grown rapidly since 2000, with over 95% of the ethanol being blended into gasoline as an oxygenate (called E10). Current 2008 production is uncertain due to the volatile economy and sharp commodity fluctuations; however, we project the final volume to be around 9.6 billion gallons (equal to about 7% of the US gasoline volume). The majority of the feedstock for US ethanol is corn (maize) grain, with a small amount (~4%) being generated from sorghum. Unlike sugarcane, which cannot be stored and for which the mills must close for several months each year, grains are easily stored for over a year and can be managed and transported in the existing infras­tructure. Another advantage of grains is that only the starch is consumed in ethanol fermentation. The protein and oil are carried through in the distillers grains (DG) and are available to go back into the livestock feed system. Nevertheless, there will be an upper limit on the land and farm resources that can be used for grain-based ethanol before impacting other commodity food markets (e. g. today the amount of grain exported from the US is about the same as that used for ethanol). Some analysts suggest that there is an impact today, others project that the maximum amount of corn that can be used for ethanol production is approximately 25-30% of the annual corn production [12]. We estimate that the upper limit will depend on how fast the expected biotechnology-driven yield increase is achieved [11, 17]. For example, we can calculate the mathematical outcome for various scenarios:

• Yield is somehow frozen today at 12 B bushels grain. E10 (oxygenate additive value) used in all US gasoline would require 15 B gal ethanol = 5 B bu grain. This would require 41% of the current corn harvest. However, 30% of that goes back into the feed system as DG so the net utilization is 29% of the available corn grain.

• Yields are projected to continue to increase due to various new technologies, with some industry experts projecting 300 bu/acre in 10-15 years: this would generate 24 B bu grain. Again assuming E10 use at 15B gal ethanol = 5 B bu grain, this would result in only 20% of the crop harvest being taken in. Accounting for the DG return, the net corn grain use would be 14%.

In reality, there are many factors which will impact the final scenario. Irrespective of the exact scenario, it seems that corn grain can provide for existing market demands plus enough grain for future oxygenate use (e. g. E10). While this is an excellent contribution, it does not meet requirements for majority replacement of gasoline volume. Obviously, to achieve further energy independence and fur­ther reduce import of foreign oil, additional renewable feedstocks are required to contribute to the total liquid fuel demand.