This study aims to compare the geographical and disciplinary coverage of OA journals in three databases: OpenAlex, Scopus and the WoS. We used the ROAD database, managed by the ISSN International Centre, as a reference database which indexes 62,701 OA active resources (as of May 2024). Among the 62,701 active resources indexed in the ROAD database, the Web of Science indexes 6,157 journals, while Scopus indexes 7,351, and OpenAlex indexes 34,217. A striking observation is the presence of 25,658 OA journals exclusively in OpenAlex, whereas only 182 journals are exclusively present in WoS and 373 in Scopus. The geographical analysis focusses on two levels: continents and countries. As for disciplinary comparison, we use the ten disciplinary levels of the ROAD database. Moreover, our findings reveal a striking similarity in OA journal coverage between WoS and Scopus. However, while OpenAlex offers better inclusivity and indexing, it is not without biases. WoS and Scopus predictably favor journals from Europe, North America and Oceania. Although OpenAlex presents a much more balanced indexing, certain regions and countries remain relatively underrepresented. Typically, Africa is proportionally as under-represented in OpenAlex as it is in WoS, and some emerging countries are proportionally less represented in OpenAlex than in WoS and Scopus. These results underscore a marked similarity in OA journal indexing between WoS and Scopus, while OpenAlex aligns more closely with the distribution observed in the ROAD database, although it also exhibits some representational biases.