Green patents and green codes: How different methodologies lead to different results

•A systematic organisation of green codes includes "IPC Green Inventory", "ENV-TECH" and "Y02/Y04S Tagging Scheme" methodologies.•“ Among 67,023 patents filed at UIBM and classified only by IPC codes, the first two methodologies identify 7.41% green patents.•“ Among 29,034 patents filed at EPO and classified by IPC/CPC code, the three methodologies identify 11.48% green patents.•"IPC Green Inventory" suits better in the UIBM dataset; "ENV-TECH" suits better in the EPO dataset.•"The three methodologies complement each other and overlap only partially. Green patents are valid instruments to measure eco-innovation which aims at reducing the negative impact on the environment and providing an efficient use of resources. There are three methodologies available to identify green patents based on the code classification: ENV-TECH (developed by OECD), IPC Green Inventory (WIPO) and Y02/Y04S Tagging scheme (EPO). Our results are: the systematic organisation of green codes for each methodology and the development of algorithms for their periodic update; the application of these methodologies to two large datasets; the comparison of the three methodologies. The relevant findings are that ENV-TECH and IPC Green Inventory should be used in combination to identify more green patents, with the inclusion of the "CPC" ENV-TECH green codes when applicable. The Tagging scheme identifies fewer green patents than the combination of the other two methodologies. The three methodologies overlap only partially (in 22.47% of cases) and their mutual integration is recommended.