This research study appraises over time impacts of public e-procurement implementation in Portugal. To attain this objective, two surveys were conducted with public contracting authorities and economic operators, in 2010 and 2012 respectively. The main contribution of this exploratory research study was to demonstrate the distinct over time perspective of public contracting authorities and economic operators and evidence that economic operators are the most vulnerable to electronic market dynamics. The research study conducted shows that the vulnerability of the economic operators results from their susceptibility to excessive price-based competition and from the additional e-procurement costs introduced by e- procurement service providers. However, in general, it is relevant to highlight that public e-procurement have a global positive impact on public contracting authorities and economic operators and in both cases it resulted in a perception of increased transparency in the purchasing procedures of public entities.