The effect of reactor pressure in the range of 0.2–2.0 MPa on the transition between the trickle-flow and the pulse-flow regime has been investigated for the non-foaming water—nitrogen and aqueous 40% ethyleneglycol—nitrogen systems. Most models and flow charts which are all based on atmospheric experiments were able to describe the transition experiments performed at 0.2 MPa reasonably well. However, this is not so at elevated pressures. For both gas—liquid systems it is found that at a constant superficial gas velocity and higher reactor pressures the transition of trickle flow to pulse flow occurs at a relative higher liquid throughput. In the pressure range of 2.5–7.0 MPa the pulse-flow regime could not be obtained for throughputs up to 1.7 cm/s superficial liquid velocity. An explanation for this effect is given based on the dynamic liquid hold-up and pressure drop data determined at the flow regime transition. Finally an empirical equation is proposed, relating the parameters governing the flow regime transition and describing the hydrodynamic conditions at the transition between trickle flow and pulse flow.