The rheological properties of a long chain branched polypropylene (LCB-PP) were investigated at the processing conditions of foam extrusion, namely high pressure, gas-loading and high shear-rates, as well as in elongational deformation. For measuring the rheological properties of PP at moderate and high deformation rates an in-line rheometer was used. Comparison of its results to standard rotational rheometry showed good agreement. The effect of the processing parameters was quantified using shift factors for temperature, pressure and gas-concentration. The influence of pressure on shear viscosity was found to be of minor importance due to an unfavorable ratio of relaxation time and residence time in the die. In contrast, shear viscosity was distinctly affected by CO2-concentration, reducing it to one third of its gas-free value at a concentration of 6 wt-% at a specific shear-rate. The change of viscosity by a variation of temperature is similar in magnitude compared to the variation due to dissolved blowing agent. Furthermore, thermo-rheological complex behaviour was observed. In the foaming process, thermo-rheological complexity could contribute to a better morphology control of long-chain branched polymers compared to linear ones. The elongational viscosity was measured using a film stretching-tool (UXF) for comparison. Distinct strain hardening was observed leading to an improved stabilisation of the foam morphology. The elongational visosity is three decades higher than the shear viscosity in the non-linear region, due to the pronounced strain hardening of the melt.