The paper provides new correlations for the estimation of the relative liquid density and critical parameters of hydrocarbons. The correlations employ molecular descriptors from computer simulation of molecular mechanics, which proved valuable in our previous work. High precision is achieved, without the use of unduly complex descriptors and rules, as a result of improved methodology. The new methodology includes a limit upon the functionality of the property database and its predesign by expanding the range and improving the distribution of the repeating structural features in the selected compounds. A compilation of estimated data for the liquid density and critical properties of some hydrocarbons of industrial importance for which no values have been available before is provided.