Process for preparing solutions of oligomeric methylaluminoxanes

The invention relates to a process for preparing solutions of oligomeric methylaluminoxanes, which contain trimethylaluminum in the free and/or complexed form, in hydrocarbons by partial hydrolysis of trimethylaluminum with water and to carrying out this process in a rotor/stator reaction machine. The product obtained is suitable for preparing highly active polymerization catalysts.