Because of the renewable nature, emission advantage, and easy adaptation, vegetable-oil-based fuels are emerging as the most promising alternatives to fossil diesel for use in compression-ignition engines. In this study, a unified approach is proposed for predicting the densities of straight and processed vegetable oils from their fatty acid composition, obviating the need of measured values particularly for use in process modeling studies. The proposed methodology has been validated using the measured densities of 11 different vegetable oils and 13 different processed vegetable oils. The predictions are found to be in good agreement (∼1% error) even at higher temperatures up to 90 °C. © 2010 American Chemical Society.