Understanding the lateral extent of a CO₂ plume has important implications with regards to buying/leasing pore volume rights, defining the area of review for an injection permit, determining the extent of an MMV plan, and managing basin-scale sequestration from multiple injection sites. The vertical and lateral distribution of CO₂ has implications with regards to estimating CO₂ storage volume at a specific site and the pore pressure below the caprock. Geologic and flow characteristics such as effective permeability and porosity, capillary pressure, lateral and vertical permeability anisotropy, geologic structure, and thickness all influence and affect the plume distribution to varying degrees. Depending on the variations in these parameters one may dominate the shape and size of the plume. Additionally, these parameters do not necessarily act independently. A comparison of viscous and gravity forces will determine the degree of vertical and lateral flow. However, this is dependent on formation thickness. For example in a thick zone with injection near the base, the CO₂ moves radially from the well but will slow at greater radii and vertical movement will dominate. Generally the CO₂ plume will not appreciably move laterally until the caprock or a relatively low permeability interval is contacted by the CO₂. Conversely, in a relatively thin zone with the injection interval over nearly the entire zone, near the wellbore the CO₂ will be distributed over the entire vertical component and will move laterally much further with minimal vertical movement. Assuming no geologic structure, injecting into a thin zone or into a thick zone immediately under a caprock will result in a larger plume size. With a geologic structure such as an anticline, CO₂ plume size may be restricted and injection immediately below the caprock may have less lateral plume growth because the structure will induce downward vertical movement of the CO₂ until the outer edge of the plume reaches a spill point within the structure. ?? 2009 Elsevier Ltd. All rights reserved.