Methane Emissions Technology to Help Achieve Net-zero Emissions Act of 2021 or the METHANE Act of 2021 This bill requires the Environmental Protection Agency (EPA) to establish standards and related requirements to reduce methane emissions from certain oil and gas facilities. Specifically, the EPA must establish methane intensity standards that become increasingly stringent over time. Initial standards must be established within four years. For purposes of establishing the standards, the EPA must categorize the facilities and base the standards on the types of methane emissions from those categories. As part of the process of establishing methane intensity standards, the EPA must establish regulations that prohibit routine flaring of natural gas from the facilities such that greenhouse gas emission from nationwide routine flaring are (1) reduced by at least 80% below 2017 levels by 2028, and (2) eliminated by 2030. In addition, the EPA must determine whether commercially available detection and measurement technologies are sufficiently robust to provide the frequency and accuracy of methane emissions monitoring, detection, and measurement to support a tradable methane intensity credit program. If the EPA determines the technologies are sufficient, then it must establish such a program. Under the program, facilities that emit more than the standards may obtain (e.g., purchase) emission credits from those that emit less. Finally, the EPA must set forth requirements concerning efforts to measure and verify the emission reductions.