A method of transmitting data in a redundant automation system, has a plurality of data transmission units and a plurality of data processing units. To possibly transmit in an especially efficient manner with the hardware resources available, a data flow characteristic of the data transmission is continuously monitored on the respective data transmission units, and depending on the data flow, data transmission is switched between the various operating modes in such a manner that an operating mode is adjusted when a synchronized data flow is detected on at least two data transmission units, the operating mode having a higher availability vis--vis the operating mode with a defective or one-way data flow on one of the data transmission units.