Physical properties and chemical components of an Alaska heavy oil from the Ugnu formation were studied by viscosity measurements, molecular beam mass spectrometry (MBMS), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR). The viscous samples rheology was measured between -10 degrees C and 60 degrees C using small amplitude oscillatory shear tests for viscosity, which generally decreases with increasing temperature. An activation energy of viscosity was measured as between 85 and 92 kJ/mol. The screening method by combined use of FTIR, NMR and a time-resolved MBMS identified several component classes: water, cyclo/straight alkanes, alkenes, mono and multi-ring aromatic molecules, as well as small fractions of other organic molecules. Azeotropic behavior was observed between 100 and 250 degrees C. The partial least squares correlation between molecular masses and the viscosity shows that water, alkylbenzene, and molecules with higher masses have positive correlations to the viscosity, but that the aliphatic molecules were anti-correlated. (C) 2012 Elsevier Ltd. All rights reserved.