The aim of this article is to develop the findings of a previous research on policies regarding proactive information disclosure, both voluntary and mandatory. We present and analyze new evidence on the factors that influence decisions taken in this respect. This study is focused on Mercosur area, a region that has received little previous research attention on these issues. To achieve the study goals, we analyze the proactive information disclosure made by local authorities, regarding both the degree of compliance with legal requirements and whether these local authorities are voluntarily and homogeneously implementing the proactive information disclosure policies recommended by the Organization of American States (OAS). Finally, with respect to the voluntary information provision, we determine the influence of environmental factors on information disclosure. The results obtained show that transparency is more an issue of attitude than of laws, and highlight the existence of a large gap between legal requirements, the OAS requirements and actual performance. Finally, it can be seen that five factors are statistically significant for the voluntary disclosure of the OAS recommended items: corruption, technology, size, mandatory disclosure policy and socio-economic development.