This article describes examples of experimental design, which is the procedure and pattern for obtaining mathematical description or mathematical model of a process or parameter under study as linear or nonlinear regression equation based on the limited number of reproducible experimental data. The examples are related to petrophysical studies of the influence of clay and carbonate contents in clastic rocks and depth of burial on porosity (passive experiment), and the influence of temperature and pressure on some principal petrophysical parameters (active experiment).