It is reported that around $6 million is spent by the producers of "Game of Thrones" to make an episode. There are no commercials on the show so how do they make money? They do it by making the show insanely popular not only in the U.S. but around the world.

If one episode costs that much then the entire season could easily rack up from $60 million to $70 million.

But the show must be making money for its producers since is it still being shown and reportedly, another season is in the making that pushes the series until 2017.

"HBO is the most profitable network in TV," said Jon Lafayette, business editor of Broadcasting & Cable. "They're known for spending a lot of money working with hot producers, spending a lot of money on content and production, and that's why people subscribe to HBO," he added.

The average gross audience of "Game of Thrones" is about 9.3 million viewers per episode. What matters with premium networks such as HBO is that viewers are glued enough to their shows to maintain their subscriptions.

According to New York Times, this TV series generates "slightly more than $1 billion annually," as compared to Showtime which is only producing $692 million.

"It is the subscription, my dear Dr. Watson," as Sherlock Holmes would put it, and not advertising.

"They don't have to make money back on advertising," said Lafayette. "HBO also has a healthy aftermarket in DVDs and online products, and that's also become a way to move HBO around the world and into markets where they don't have the HBO channel," he added.

And that is why some TV series are concerned with piracy. In this regard, the TV series has been one of the most pirated HBO shows in the world.  But surprisingly, that doesn't even make a dent in the producers' income, not in the long term or on the subscribers' side.

So if "Game of Thrones" makes $1 billion annually, it should have earned at least by now around $4 billion to $5 billion since it premiered in April, 2011.