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Abstract: Bubble column reactors are widely used in many industrial applications due to their simplicity and safety of operation. Despite these advantages, the design and scale?up of bubble column reactors is still challenging especially for industrial conditions at elevated pressure and temperature. One reason is the uncertainties concerning the specific interfacial area which is directly dependent on the bubble size distribution, bubble velocity, and gas hold?up. All these parameters are difficult to measure under industrial conditions due to the opaqueness of the bubbly flow and the safety risks of using organic solvents at elevated pressures and temperatures. This article introduces endoscopic bubble image velocimetry, a new measuring method that enables the detection of bubble sizes and bubble velocities in organic solvents at elevated pressure and temperature (pmax?=?1.85?MPa and Tmax?=?70?°C) for maximal gas hold?ups of 16?%. For this system it becomes evident that the bubble size distribution for low superficial gas velocities is almost unaffected by pressure and temperature, whereas the bubble velocity decreases slightly.