Carbon capture and storage (CCS) technology has been considered as an important method for reducing greenhouse gas emissions and for mitigating global climate change. Three primary options are being considered for large-scale storage of CO₂in subsurface formations: oil and gas reservoirs, deep saline aquifers, and coal beds. There are very many large saline aquifers around the world, which could make a big contribution to mitigating global warming. However, we have much less understanding of saline aquifers than oil and gas reservoirs. Several mechanisms are involved in the storage of CO₂ in deep saline aquifers, but the ultimate goal of injection of CO₂ into the aquifers containing salt water is to dissolve the CO₂ in the water. So it is important to study the solubility trapping and sensitivity factors of CO2 in saline aquifers. This paper presents results of modeling CO₂ storage in a saline aquifer using the commercial reservoir simulator ECLIPSE. The objective of this study was to better understand the CO₂/brine phase behavior (PVT properties) and quantitatively estimate the most important CO₂ storage mechanism in brine-solubility trapping. This would provide a tool by performing theoretical and numerical studies that help to understand the feasibility of CO₂ geological storage. A 3-dimensional, 2-phase (water/gas) conceptional reservoir model used finite, homogenous and isothermal formations into which CO₂ is injected at a constant rate. The effects of main parameters were studied, including the vertical to horizontal permeability ratio k_v /k_h, salinity, and residual phase saturations. The results show that the vertical to horizontal permeability ratio has a significant effect on CO₂ storage. Moreover, more CO₂ dissolves in the brine at lower k_v /k_h values.