CO2 with only a small risk of surface leakage in the following 10,000 years. However, the level of uncertainty of these estimates depends on the formation (type and heterogeneity), the physical and chemical processes accompanying CO2 storage, the method being used to determine the storage capacity and the amount of available data. Several assessments of regional storage capacity were conducted in Europe, China, Japan, Canada, and the United States, yet making direct comparisons of their results poses a problem due to their different underlying assumptions. A method to better assess the CO2 storage capacity worldwide using globally available datasets was developed at MIT as part of a larger project to use Integrated Assessment Models (IAMs). CO2 sequestration via solid gas hydrates (clathrates), including storage in deep oceanic basins, sediments under the sea floor, permafrost regions, methane hydrate reservoirs, and depleted oil and gas fields partially saturated with water, has received increased attention in the past years due to its potential storage capacity in the hundreds of thousands of Gt. Amongst the options for CO2 storage, deep saline aquifers are one of the best candidates because they are commonly found throughout the world, often have large storage capacity and ideal geologic properties, are unsuitable for human consumption or agriculture, and are isolated from the biosphere. However, this process involves complicated reaction networks among CO2, brine solution and rock formations, which could potentially affect the integrity and storage efficiency of the well over long term. The efficiency of trapping mechanisms and the movement of CO2 through the rock are strongly influenced by the CO2-brine-rock wettability, the pressure and temperature, salinity and dissolved ions. These trapping processes take place at different rates and over many years, even thousands of years. The use of former fossil fuel reservoirs for geo-sequestration of CO2 is attractive for many reasons. Rock reservoirs have sufficient porosity and permeability to promote massive CO2 volume injections while oil and gas fields have a geological barrier preventing upward migration and leakage of CO2 into shallower formations (proven by having stored hydrocarbons for thousands to millions of years without appreciable leakage). Meanwhile, the existing infrastructure and industrial setup required for fluid injection can be utilized while the reservoirs have already been geologically characterized, tested, and monitored; Revenues from the produced gas/oil can be used to help offset the current high costs of CO2 sequestration. However, sequestering CO2 while extracting oil or gas is probably not the best way to mitigate the environmental impact of CO2