1. A method for developing models to predict physical or chemical properties of a petroleum fluid when such properties of such fluids cannot be measured by conventional analytical methods comprising the steps of a) determining one or more models that predict one or more predetermined properties from a set of oils whose optical spectra and properties are known wherein a model corresponds to each predetermined property which is related to the spectrum, b) estimating the quality of the models, c) estimating the predictive quality for samples with unknown properties, d) augmenting the spectrum with shape parameters and/or properties that are predicted by step a, and e) determining the quality and predictive quality of the models after step d.