Dan Marks, a research fellow in energy security at the Royal United Services Institute (RUSI), said major oil producing nations have always been wary of policies which aim to squeeze the supply of fossil fuels because “they have interests they need to protect”. For Saudi Arabia these interests include almost 300 billion barrels of oil in their vast reserves. The kingdom represents almost a fifth of the world’s oil reserves, and is the de facto leader of the Organization of Petroleum Exporting Countries which together represent almost 80% of the world’s oil. The fundamental premise of a fossil fuel phase out would destabilise these petrostates by setting in motion a series of policy changes among global regulators, heightening investor concerns over so-called ‘stranded assets’, Marks told the Guardian. “This is why the world’s most important oil producing countries have always said ‘you tackle demand, you don’t tackle supply’,” he said.