The Canary Islands are the only Spanish territory that holds potential for high enthalpy geothermal resources, although there is no evidence in the islands of hydrothermal fluid discharges in the surficial environment except for Teide volcano fumaroles in Tenerife. We herein report the results of several diffuse carbon dioxide (CO2) degassing surveys carried out at six mining licenses across Tenerife (Berolo, Guayafanta, Abeque, Garehagua and Garehagua II) and Gran Canaria (Atidama), covering a total of 640 km(2) and more than 3230 sampling sites. Selected geochemical molar ratios, spatial distribution of CO2 efflux, statistical-graphical analysis of CO2 efflux, isotopic composition of CO2 (delta C-13-CO2), the calculated volcano-hydrothermal contribution of CO2 and the deep-seated CO2 efflux were studied. These data were combined and used for geothermal exploration, demonstrating an effective reconnaissance strategy that reduces risk and cost. Garehagua II, Garehagua (both located in the north-south volcanic rift of Tenerife) and Abeque (located in the northwest volcanic rift of Tenerife) are, in this order, the mining licenses studied that showed the highest potential to contain geothermal resources, based on the geochemical indicators ranking proposed. (c) 2020 Elsevier Ltd. All rights reserved.