Here is another presentation that I made some time ago. It was presented initially to the petrophysics community in my company and later on to a wider audience consisting of geologists, geophysicists, reservoir engineers as well as others. The objective of this presentation was to clarify the different types of porosity, namely total porosity and effective porosity computed by petrophysicists. There is a confusion or misunderstanding of the petrophysical definitions of porosity, which are somewhat different from those understood by geoscientists and reservoir engineers. Although we petrophysicists may be practitioners of the “Dark Art”, as mentioned by some readers on LinkedIn, we are not able to distinguish between connected and unconnected porosity, when we analyze standard logs. To make it more confusing, there are other definitions of porosity, like open porosity and closed porosity, as used in some countries. I hope that my fellow professionals, especially the younger ones, will find this presentation worth reading.