One of the fundamental provisions of the European electricity directives is the so-called unbundling of structures and functions. Vertical disintegration with Full Unbundling (ownership unbundling or independent system operation) is considered an important step toward electricity market restructuring. While Full Unbundling (FU) models appear to be the most prevalent, several European countries adhered solely to less stringent forms of unbundling. Using a dataset of the 35 major electricity transmission utilities in Europe, this study provides an econometric analysis to understand the individual effect of regulation and ownership structure on the decision to adopt more stringent unbundling regimes. The overall results show that incentive-based or hybrid regulatory schemes and private ownership, are associated with a higher probability that a country will opt for FU.