Aramco is a monster.

As The Economist noted, the company produces 10 million barrels of oil each day, a number equivalent to the US's entire daily output, and has 10 times more oil reserves than Exxon.

Aramco is also very good at what it does. Saudi Arabia's break-even price for oil production is a mere $15 a barrel, second-lowest only to Kuwait and well below oil's current $32-per-barrel price, according to The Economist.

There are any number of reasons why Aramco would go public, which range from encouraging investment in the Saudi stock market to bringing some limited transparency to a notoriously opaque company. But the biggest reason just might be revenue generation.

According to The Economist, Aramco would be selling "perhaps 5%" of the company to investors. Five percent of, say, $1.5 trillion is still $75 billion. Saudi Arabia might need the cash.