Random House USA has sold nearly 20 million books in E.L. James’ Fifty Shades of Grey trilogy, according to a Wall Street Journal report by Jeffrey Trachtenberg.

The books—which went on sale in March and April—have brought in a whopping $145 million in revenue for Random House imprint Vintage, with the trilogy currently accounting for “one in five adult-fiction physical books sold in the U.S.”

Random House, Inc. also has rights to the books in the UK, Australia, and India, where the trilogy is published by its Arrow imprint, as well as in Germany and Spain.

According to the WSJ report:

By comparison, Stieg Larsson’s best-selling “The Girl With the Dragon Tattoo” trilogy took more than three years to reach the 20-million sales mark in the U.S. Those three books were released in the U.S. in 2008, 2009 and 2010.

Around the world, the “Fifty Shades” books have sold a total of 31 million copies in English-language markets, including the U.S., according to a spokesman for Vintage. Movie rights have been acquired by Comcast Corp.’s Universal Pictures and Focus Features.

In the U.S., sales have been split nearly evenly between physical and digital versions, with 9.8 million paperbacks sold through July 2, compared with 9.6 million e-books during the same period, Vintage says.

The numbers are so huge that I suspect Random will see its U.S. profits nearly double in 2012 as a result. Random House’s entire world-wide operating revenue for fiscal year 2011 came to 1.7 billion euros (a slight fall from 2010), with operating earnings before interest and taxes of €185 million ($246.5 million). Though parent company Bertelsmann does not break out U.S. earnings in its annual report (PDF), it does disclose that the U.S. accounted for 53.8 percent of its 2011 revenues. With just four months of sales producing $145 million in revenue, it’s clear that James’ series will have a major impact on company profits.

Impressed by the sales of the trilogy, I asked a Random House staffer who worked on the series if he thought a doubling in profits might be possible. “I don’t know about that,” he replied. “Let’s just say we could take the rest of the year off and still make our numbers.”