CO2 emissions in the atmosphere are increasing continually, which are mainly originated from burning of fossil fuels. The fossil fuels are expected to remain a major component of the world's energy supply in the near future, because of their inherent advantages. Therefore, various measures have to be considered to reduce anthropogenic CO2 emissions. Increasing the efficiency of energy usage and/or developing lower carbon or non-carbon energies to replace high carbon fuels may bring the result of the reduction of the accumulation of CO2 in the atmosphere. The other alternative to reduce CO2 concentrations in atmosphere include gaseous storage in various deep geological formations, liquid storage in the ocean, and solid storage by reaction of CO2 with metal oxides to produce stable carbonates. In this article, the geological storage options of CO2 are examined. They are discussed in terms of applicability, cost, storage capacity and safety. (C) 2010 Elsevier Ltd. All rights reserved.