This one relates to the little multicolored maps on the backs of seed packets. The ragged stripes stretching from east to west are growing zones: regions where water supply, temperature and sunlight make hospitable climates for certain types of plants. If you live in Zone 5, for example, you will likely have trouble growing a plant that requires the long growing season and high heat of Zone 10 [source: Burpee].
Biofuel crops are no different from petunias or peppers in this regard. Certain crops will grow better in certain regions and may not grow at all in others. And while the range of oil-producing crops considered viable for biofuel production is wide enough to fit most growing zones, the most productive crops simply won't grow everywhere. Consumers living in a low-producing region would need to have biofuel trucked or piped to them, increasing both cost and the amount of emissions produced in production and transport [source: Pimentel].
Researchers are working to increase biofuel yields from weather-tolerant crops [source: Lau]. But in much the same way that oranges will never be a cash crop in Alaska, there will always be some regions that simply can't support large-scale production of biofuel-rich crops.