Partial Least Squares (PLS) calibration models for viscosity, asphaltene content and Total Acid Number (TAN) based on Gas Chromatography (GC) and Infra Red (IR) spectroscopy have been compared based on predictive quality, and also based on chemical significance. Crude oils and condensates, 20 in total, originating mainly from the North Sea, have been analysed and PLS calibration models have been built. The models based on IR data gives somewhat better predictions. Biodegradation is an important factor for the variation in TAN values, and there are indications that biodegradation has some effect on the variation of asphaltene content as well. (C) 2013 Elsevier Ltd. All rights reserved.