Coal, the most abundant fossil fuel, is also the worst emitter of carbon dioxide, watt for watt. Coal burning generates 41 percent of the world's carbon dioxide emissions from energy use. And coal use is projected to rise steeply (see "China's Coal Future," January/February 2007). A new MIT report--The Future of Coal: Options for a Carbon-Constrained World--describes a variety of advanced coal technologies but recommends that they be accompanied by technologies to capture and sequester carbon dioxide on a staggering scale. There "do not appear to be unresolvable open technical issues" surrounding feasibility and safety of sequestration, the report says; any hurdles "appear manageable and surmountable." The report contains suggestions about where the U.S. and China might begin putting all the carbon dioxide; in China's case, prospective storage areas (below) are ranked in order of priority for study. All are sedimentary basins; their ranking is based on geologic complexity and proximity to carbon dioxide sources. Yellow is highest priority, followed by orange, blue, and pink.