This article presents a selection of results obtained with the FHYD program. This software allows simulation of mixtures composed of petroleum fluids and water, with determination of the nature of thermodynamically stable phases (oil-gas-water-hydrate) under given conditions of temperature and pressure, along with the quantity, composition and properties of these different phases. Additionally, the program can automatically produce phase diagrams. Several examples of these have been included here, ranging from binary systems (water-ethane) and ternary systems (water-methane-propane) to the most complex petroleum fluids. The presence of dissolved salts (sodium chloride) has also been taken into consideration, as well as the calculation of conditions for the deposition of solid salt. A number of petroleum problems are highlighted: water-saturated separator gas, water-saturated oil in reservoir conditions, and oil in the presence of salt water. Estimates for the quantities and the composition of hydrates formed are compared with experimental data and with results obtained using other software. The FHYD program can serve to give a more realistic representation of petroleum fluid behaviour with more accurate determination of the transportation properties of their different phases, which is essential for the new generation of simulation models for multiphase pipeline design and operation.