The viscosity and surface tension of n-heptane-insoluble asphaltenes and asphaltene-vacuum residue blends were determined by measuring the forces on liquid bridges between thin films. Asphaltenes from a variety of heavy oils and bitumens gave surface tensions in the range of 15-19 mN/m at 358 degrees C and viscosities of 9-16 Pa s. At temperatures above ca. 400 degrees C, the viscosity increased to as much as 70 Pa s because of cracking and coke formation, whereas the surface tension declined to values as low as 5 mN/m. The properties of vacuum residues and blends of residue and asphaltenes all approached the properties of the asphaltenes at high temperature, because of extensive cracking and devolatilization. The contact angles of the asphaltene melts were in the range of 18 degrees-57 degrees on Ni/Fe and coke surfaces. The differences in fluid properties between asphaltenes did not correlate with the average chemical characteristics.