Flow mechanisms in trickle beds operating in dispersed bubble and pulse flow are discussed in detail including theoretical considerations and literature results. The possible local flow patterns are then compared to experimental investigations made in a laboratory scale trickle bed by means of the electrochemical shear rate sensor technique. In the gas-rich slugs of pulse flow the flow mechanism is analogous to trickle flow. In the liquid-rich slugs of pulse flow and in dispersed bubble flow, our results as well as literature data can be explained by a flow mechanism in which the liquid flow is dominated by viscous forces and the gas bubbles pass through the constrictions of the porous media by pressure pulses.