Abstract Electrical conductivity is a parameter which can be used for monitoring the entire hardening process of oilwell cement slurries. The theoretical relationship between conductivity, porosity, cement chemistry, and ion content is discussed. The theory is confirmed by experiments; basically, the cement slurry conductivity decrease is a function of porosity decrease. The applied results show that the electrical conductivity of a curing slurry reflects both the strength development and the ability to resist gas migration.