Over the last few years, governments worldwide have started to develop and implement open data initiatives to enable the release of government data in open and reusable formats without restriction or charge for their use by society. As a result, a large number of open data repositories, catalogues and portals have been emerging in the world. The efficient development of open data portals makes it necessary to evaluate their quality systematic, in order to understand them better and assess the various types of value they generate. Citizens also expect data disclosed by official authorities to have quality in the sense that they are official data and therefore should be accurate and reliable. Consequently, the aim of this paper is to examine and compare the quality of these portals. For this purpose, a benchmarking framework is proposed and validated to evaluate the quality of open data portals on the national level. The results obtained show that the number of datasets online and the sophistication of open data portals and their functions differ, reflecting the lack of harmonization and the need for quality standards. In particular, the United Kingdom, India and the United States have published many datasets and launched advanced portals.