Subject to various assumptions and corrections, values of apparent porosity can be derived from any neutron log. One can not underestimate the slow down of neutrons by other elements even if they are less effective. Certain effects, such as lithology, clay content, and amount and type of hydrocarbons, can be recognized and corrected for only if additional porosity information is available, for example from sonic and/or density log. Any interpretation of a neutron log alone should be undertaken with a realization of the uncertainties involved.