Chapter 9 by M. G. Tertr and B. Saveyn provides an estimate of the investment needs and additional costs of bringing the EU’s dependence on fossil fuels from Russia to zero by 2027, with a specific focus on natural gas. This analysis was used to prepare the REPowerEU plan presented by the Commission on the 18th of May 2022. Decoupling the EU from Russian fossil fuel imports has already begun and will pass through various stages affecting both demand and supply. From this perspective, the analysis indicates that implementing the full potential to reach zero-dependence could require 300 billion euros cumulative from now to 2030—which is beyond the Fit for 55 proposal. By the end of 2027, this transition could correspond to approximately 210 billion euros in investment. These REPowerEU investments correspond to about 5% of the total Fit for 55 investments up to 2030 and would come in addition to them. The Commission analysis estimates that the Fit for 55 and REPowerEU measures combined could save the EU 80 billion euros annually on gas imports, 12 billion euros on oil imports, and 1.7 billion euros on coal imports.