Because the literature of European economic history has paid little attention to traditional electricity systems, the interest in studying Fensa lies in analysing the different types of companies, which helped to shape the development of the Spanish electricity sector prior to its present oligopolistic structure. This case provides insight into two issues. First, we learn about the behaviour of the second-generation companies (those that based their production on a controlled hydropower regime), which, despite their limited size, made their commercial specialisation (supplying the dynamic industrial market of Guipúzcoa) their main comparative advantage. Second, we analyse the behaviour of those companies which at this time, as distribution companies and/or subsidiaries of the large Spanish companies (Iberduero), were an instrument of the policy of integrating regional markets.

The study of the Irati hydroelectric company aims to show some of the business strategies behind the first stages of the development of electricity in Spain and, in turn, pose new questions regarding the factors and conditioning elements of the country's regional industrialization processes. In fact, this firm represents one of the many possibilities electricity brought to non-industrialized Spanish regions at the start of the 20th century. The electricity generated by its falls explains the creation of Spain's largest integrated industrial complex built up around the initial processing of timber (saw-mills and chemical distilling) and its commercialization (railways), along with the sale of its energy surpluses on the most important market in the region of Navarre. Furthermore, the analysis of this latter activity allows us to offer an explanatory model that is both an alternative and a complement to the classical model —that provided by the largest firms—concerning the progressive incorporation of the traditional electrical markets into the integrated markets of the major Spanish companies.

Over the past two decades it has been questioned whether the electric utility industry is a natural monopoly. Electricity generation is no longer considered a natural monopoly and the topic is debated in relation to electricity distribution. This article explores the main contributions in this field in order to apply their findings to the Spanish Electric Utility Industry in the inter-war period. The study focuses on one of the major Spanish companies, Sociedad Hidroeléctrica Española, and shows that generation, transmission and distribution of electricity were. natural monopolies. The results indicate that the monopolistic structure which the inter-war electric utility industry exhibited was the optimal form of organisation.