Two nominally identical pure bitumens, commonly employed for pavement construction in the United Kingdom, were tested in uniaxial tension, compression, and shear, over a wide range of temperatures, stresses, and strain rates. The bitumens were found to exhibit linear viscous behavior at low stress levels, and power-law creeping behavior at higher stress levels. The temperature dependence was found to follow the Arrhenius relationship at temperatures immediately above the glass transition and the Williams, Landel, and Ferry (WLF) equation at higher temperatures. Below the glass transition temperature, the Eyring plasticity model was found to hold. Constitutive models that reflect the physical mechanisms of steady state and transient deformation are proposed. The fracture properties of the bitumens are also discussed.