Abandoned oil and gas wells are both potential crucial sources of methane emissions and capacity for carbon storage. Numerous and continuously growing numbers of global abandoned oil and gas wells can be a key obstacle in delivering the Paris Agreement goals of keeping global warming below 1.5⁰C. Abandoned oil and gas wells worldwide will continue releasing methane into the atmosphere without effective cleaning-up strategies, but the actual numbers, methane flux, and geology-related details of them remain poorly understood. Here, we developed a resource-type-specific and complete emission inventory for global abandoned oil and gas wells at the well/state/territorial/country levels, covering 4.5 million abandoned wells worldwide by 2020, 9% of which are identified individually in terms of emissions and well-level details. According to our estimate, annual methane leakage of global abandoned oil and gas wells is about 0.4 million tons in 2022, which is 1% of total global oil and gas sector methane emissions, 70% of which come from abandoned wells in the United States. There are strong characteristic heterogeneities among abandoned oil and gas wells in terms of terrain, resource type, plugging status, geographical location and so on. Timely plugging of those abandoned wells is critical for eliminating methane leakage from abandoned wells, particularly from historically major oil and gas producers, which could potentially reduce global cumulative emissions from this source by 31% during 2022 to 2050.