Record crop prices are signaling the world's farmers to produce more. The recent prospective acreage report released by the USDA shows that the ability of U.S. farmers to grow more is limited by a lack of land. The USDA projects that acreage planted to crops in the United States will increase by about 1 percent in 2008 relative to 2007 acreage and about 2.5 percent relative to 2006 acreage. This lack of a supply response by U.S. farmers shows how insensitive aggregate U.S. planted acreage is to price changes, at least in the short run. It explains why introducing a major new demand for agricultural output in the form of biofuels should be expected to have such a large impact on commodity prices.