Donald Trump has said that "if elected, he might halt purchases of oil from Saudi Arabia and other Arab allies unless they commit ground troops to the fight against the Islamic State or 'substantially reimburse' the United States for combating the militant group."

So just how much money has the U.S. sent to the Saudi kingdom by way of oil purchases?

While U.S. crude oil imports from Saudi Arabia have declined substantially over the past decade, they remain above 1 million barrels per day.

Converting the historical oil imports from 1973 to 2015 into constant dollars using inflation-adjusted average annual oil prices over this time frame yields a total wealth transfer of US$1.02 trillion in 2015 dollars.