Just how much of America's debt does Saudi Arabia own? Well, It is a secret of the vast US Treasury market, a holdover from an age of oil shortages and mighty petrodollars.
But now that question—unanswered since the 1970s, under an unusual blackout by the US Treasury Department—has come to the fore as Saudi Arabia is pressured by plunging oil prices and costly wars in West Asia.
A big risk is that the kingdom is selling some of its Treasury holdings, believed to be among the largest in the world, to raise needed dollars. Or could it be buying, looking for a port in the latest financial storm? As a matter of policy, the Treasury has never disclosed the holdings of Saudi Arabia, long a key ally in the volatile West Asia, and instead groups it with 14 other mostly Opec nations including Kuwait, the UAE and Nigeria. For more than a hundred other countries, from China to the Vatican, the Treasury provides a detailed breakdown of how much US debt each holds.
"It's mind-boggling they haven't undone it," said Edwin Truman, the former Treasury assistant secretary for international affairs during the late 1990s, and now a senior fellow at the Peterson Institute for International Economics in Washington. Because relations were rocky and the US needed their oil, the Treasury "didn't want to offend Opec. It's hard to justify this special treatment for Opec at this point".
Representatives for the Saudi Arabian Monetary Agency, known as Sama, and the nation's finance ministry declined to comment.
Apart from the kingdom itself, only a handful of Treasury officials, and those at the Federal Reserve who compile the data on their behalf, have a clear picture of Saudi Arabia's US debt holdings and whether they are rising or falling.
For everyone else, it is a guessing game.
Sama's own figures show reserve assets held in foreign securities have fallen by a record $108 billion in 2015. The Saudi central bank, which doesn't disclose separate figures for Treasuries, owned $423 billion in overseas securities as of November.