Electronic government procurement (eGP) is quickly becoming an essential piece of national e-government programs, since it enables active transparency and favors efficient vendor relationships; however, little attention has been paid to the need for periodical measurement of eGP portals' performance and goal satisfaction. Although maturity levels schemes have been proposed for other domains, most notably ITrelated, to the best of our knowledge no maturity level model of eGP has been widely deployed yet. This articlepresents the e-Government Procurement Observatory Maturity Model (eGPO-MM), which focuses on both legal and institutional arrangements, and portals' technical aspects; the model consists of two Leverage Domains, seven Key Domain Areas, and 25 Critical Variables, which are valued with a weighted scoring system that produces quantitative indicators about portal capabilities and allows direct comparisons. The model was  used to evaluate eGP portals from 14 countries in Latin America and the Caribbean; the measurements are presented, and fit well with previous rank perception, leading to a good reception by participant agencies. eGPO-MM has already allowed to identify areas for joint action and fostered knowledge-sharing among governments, including identification and dissemination of e-procurement best practices; it also established clear reference points to allow each agency to determine a roadmap to higher e-procurement maturity.