Several possible mechanisms for generation of high electrical potentials in supersonic nozzles are examined. It is suggested that charge transfer between condensate particles and the probe, due to a contact potential, occurs during particle—probe collisions. A high electrical‐probe potential develops as the kinetic energy of the charged particles in the gas flow is converted to electrical energy. This conversion is possible because the particles are massive and have a low mobility. It is suggested that particle mobility and probe voltage—current measurements can yield size and energy information about the condensate particles.