Ironically, however, one of the main problems with using CO₂ for oil recovery is its scarcity. Capturing the gas from power station smokestacks or volcanoes is not cheap, and the cost of capturing it from smaller sources, such as cars or even most industrial plants, is prohibitive. Another hurdle is transportation, which can be too costly if the oil fields are in remote regions.

Chemistry-based recovery is a more recent strategy. Certain chemicals can mix with trapped oil and make it less viscous, so that it can flow toward the well. These substances all work on the same principle, which is similar to how layers of soap molecules engulf fatty substances and work to remove grease from your hands. The most successful chemical process also increases the viscosity of the underground water, which helps the water push the oil toward the wells without reaching the wells first. At China’s Daqing oil field, this process is credited for getting out an extra 10 percent of the reservoir’s oil since the mid-1990s. And in one version of the process, a caustic solution generates the soaplike materials from components present within the oil itself, limiting the overall cost.

   
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