Filled or empty tubular reactors have been at the heart of many chemical processes in academia and industry. Understanding the phase behavior in such reactors is essential to improving the conversion and selectivity of a given chemical transformation and to minimizing energy consumption. This study shows that the pressure-drop method is a simple and effective technique for measuring vapor liquid phase equilibria at temperatures of up to 573 K. The basis of the pressure-drop method is flowing the fluid through a capillary with a relatively small inner diameter. The pressure drop between the inlet and outlet of the capillary depends on the phase state of the fluid (gas and/or vapor). In this article, pure propan-2-ol and the binary system propan-2-ol + water have been investigated to validate the method at high temperatures for these fluids. The binary system water + acetonitrile was then measured to demonstrate that the phase equilibrium of a thermally reactive mixture can also be determined by using the pressure-drop method. We have modeled the experimental pipeline pressure-drop results with the Process Systems Enterprise gPROMS ProcessBuilder 1.1.0 modeling environment using the Peng-Robinson equation of state and the superTRAPP algorithm for transport properties, and we find that the theoretical calculations are in good agreement with the experimental results.