Mercury has been one of the most persistent cases in contemporary history of international market regulations and this in spite of its having been affected by important technological changes and the regular discovery of new deposits. This paper offers an approach to the least known period, although perhaps the one in which the greatest rises in process and production occurred as a consequence of market manipulation. The period coincides with a series of agreements between the Spanish and the Italian producers and the outcome was a worldwide cartel known as “Mercurio Europeo” which came into being in 1928. The aims of this work will, therefore, be first to describe the features of the various stages of development of the international mercury market during the first half of the twentieth century, with emphasis on the characteristics and conditioning factors in each period. Secondly, the objective is to analyze the various market agreements that came about, the effectiveness of the clauses therein, the construction of distribution networks and the influence that the increase in production had on other mines and on certain technological developments.