Congestion, which occurs when network users cannot obtain the capacity contract they need to flow gas, emerged at 50 interconnection points in 2022 following tight market conditions and the need to reroute gas flows away from historic east-west routes to predominantly west-east routes in Europe (with the Russian invasion of Ukraine), according to the European Union Agency for the Cooperation of Energy Regulators (ACER). The volume of unsuccessful requests amounted to nearly 40 TWh/d in 2022, which is about two and a half times the technical firm capacity at the congested points, and a 40-times increase from a level of 1 TWh/d in 2021. Consequently, congestion revenues collected by TSOs rose sharply from €55 million in 2021 to around €3.4 billion in 2022.