Europe has reduced its reliance on Russian oil, but geological limits on global oil production could become the next major challenge to long-term energy security.

Since Russia’s full-scale invasion of Ukraine, the European Union (EU) has altered its approach to energy security. It has reduced its dependence on Russian oil through diversifying its supplier base and accelerating the deployment of renewable energy. These efforts have strengthened Europe’s capacity to resist coercive energy diplomacy. Yet Europe’s energy transition has not eliminated its dependence on imported oil. Oil remains essential for transportation, industry, and petrochemicals, and the EU continues to rely heavily on external suppliers to meet its energy needs. In 2025 alone, the European Union imported approximately 435 million tonnes (Mt) of crude oil, valued at more than €212 billion.

Much of Europe’s energy security debate has focused on geopolitical disruptions, and far less attention has been paid to an equally important challenge: the terminal decline of oil production in exporting countries. Terminal decline refers to a period during which production transitions to an irreversible downward trend after reaching a peak. The natural oil supply is finite because the slow natural processes involved in its formation occur at a slower rate than the rapid rate at which it is extracted. The difference between resource formation and extraction rates leads to the gradual depletion of available resources.

Unlike wars or sanctions, terminal decline does not create an immediate supply shock. Instead, it gradually reduces the amount of oil available for export. As more exporting countries pass their production peak, fewer producers will be able to increase output when markets tighten, or supply disruptions occur. For an import-dependent region such as the European Union, this means that diversification alone may become increasingly difficult over time.

This challenge is already affecting several of Europe’s oil suppliers. Azerbaijan, which supplied approximately 4.1 percent of the EU’s crude oil imports in 2025, has been in terminal production decline since reaching peak output more than a decade ago. Other important suppliers are confronting similar trends, including Nigeria (5.8 percent of EU crude oil imports), Algeria (3.7 percent), and Mexico (2.2 percent), all of which have experienced declining production from mature fields. Going forward, additional exporting countries are expected to enter this phase as their largest oil fields age and depletion accelerates. These declines raise an important question: how should Europe prepare for a future in which an increasing share of its oil suppliers are producing less oil each year?

Europe’s Plan for Long-Term Oil Supply Decline 

The REPowerEU Plan, introduced in 2022, established the foundation for strengthening Europe’s energy security through diversifying energy supplies, accelerating renewable energy deployment, and reducing dependence on Russian fossil fuels. While these policies have greatly improved Europe’s resilience, the European Union has to adapt its policies to address long-term geological constraints on global oil supply.

The European Union should make the decline of terminal oil production a regular part of its energy security assessments. Considering geopolitical risks, policymakers should track production trends, the maturity of major oil fields, and the long-term export capacity of key supplier countries. Understanding which suppliers are likely to experience declining production will help the EU identify future weaknesses before they become crises. Long-term energy partnerships should be guided not only by current export volumes but also by the sustainability of future supply. The most effective way to reduce Europe’s exposure to terminal oil production decline is to reduce its dependence on imported oil altogether. Persistent investment in electrification, renewable energy, and energy efficiency will strengthen Europe’s long-term energy security while supporting its climate objectives.

The European Union has already shown that it can respond decisively to international energy crises. It should apply the same strategic perspective to the slower challenge of terminal decline in oil production. The question is no longer whether Europe can diversify away from a single supplier, but whether it is preparing for a future in which many of its suppliers will gradually produce less oil. Recognizing that challenge today will leave Europe better positioned to safeguard its energy security in the decades ahead.

About the Author: Dr. Yagiz Sullu

Dr. Yagiz Sullu is the founder and lead analyst of Sullu Strategic Advisory LLC. He recently earned his PhD in planning, governance, and globalization from Virginia Tech, where his research examined the relationship between energy resources, political institutions, and geopolitical risk in oil-producing states. His work focuses on energy security, international political economy, governance, and strategic risk, with regional expertise spanning Europe, Eurasia, the Middle East, and Africa. He previously served as a research associate at the Washington Institute for Business, Government, and Society.

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