One of the oil world’s longest and best kept secrets may finally be revealed. Saudi Arabia is preparing to unveil how much oil it holds, a closely guarded state secret that has been kept quiet for decades. 

The decision to bring such important data to light comes as Saudi Aramco is preparing to partially privatize its assets, an IPO that could bring in some $100 billion. The IPO will be a monumental event, one that the Wall Street Journal says could offer Wall Street some of the largest fees in history. 

Saudi Arabia often trades off with Russia – and more recently, with the U.S. – as the world’s largest oil producer. But while it produces at similar levels as Russia and the U.S., it is long been a vastly more influential player in the oil world. That is because of two reasons – the size of its reserves, and the ability to use latent spare capacity to quickly adjust supply, affording it an outsized influence on crude oil prices. 

But while everyone believes Saudi Arabia has some of the largest oil reserves in the world, perhaps rivaled only by Venezuela, there has been a lot of uncertainty and skepticism over exactly how much sits beneath the Saudi desert. The world’s largest oil field, Ghawar, has been producing since the 1950s, raising speculation about the longevity of the supergiant oilfield. It alone is thought to hold around 

, and it churns out more than 5 million barrels every single day. Surely, it cannot continue like this indefinitely, but the Kingdom has not revised its official reserves for years, which have stood at 260 billion barrels since the 1980s. It is hard to overstate how valuable this information is, and how fiercely Saudi leadership protected it. 

However, the collapse of oil prices since 2014 has pushed the Saudi budget deep into the red. The Deputy Crown Prince Mohammed bin Salman is undergoing an historic transformation of the Saudi economy, a multi-decade plan to diversify the country’s economic base and create new sources of revenue. At the heart of the plan is spinning off roughly 5 percent of Saudi Aramco, the most valuable oil company in the world. Saudi officials believe that the company is worth between $2 and $3 trillion.