This paper develops a methodology to compare the quality of examination services across patent offices. Quality is defined as the extent to which patent offices comply with their patentability conditions in a transparent way. The methodology consists of a two-layer analytical framework encompassing “legal standards” and their “operational design”, which includes several interdependent components that affect the stringency and transparency of the filtering process. The comparison of patent offices in Europe (EPO), Japan (JPO) and the US (USPTO) shows that their operational designs differ substantially: the EPO provides higher-quality and more expensive services than the USPTO, while the JPO is in an intermediate position. These results illustrate that different system designs lead to different outcomes in term of backlogs, patent propensity and the number of dubious patent rights in force. In this respect, they: 1) provide an empirical validation of Jaffe and Lerner's (2004) conjecture of a vicious cycle between quality of examinations and demand for patents; and 2) highlight the need for a multi-faceted convergence of patent systems before mutual recognition is put in place.