In this work, a corresponding-states correlation is presented for prediction of crude oil density in an undersaturated state. The correlation is the extension of corresponding-states liquid densities correlation. The modified corresponding states liquid densities method for predicting saturated liquid densities was coupled with the Tait equation to predict undersaturated densities. Correlations are proposed for the temperature-dependence of Tait equation parameters. Applying proper mixing and combining rules, we calculated the density of 26 crude-oil samples, mainly from Iranian reservoirs. The mixtures included a variety of compositions including N-2, H2S, CO2, and hydrocarbons. The AAD% for the present method is 0.85%.