High-value prisoners in Guantanamo Bay’s Camp 7 are partial to E. L. James’ “Fifty Shades of Grey” series, according to U.S. congressman Jim Moran, who recently visited the facility.

Moran, who was among the congressional delegates who visited Guantanamo Bay last week, told the Huffington Post that the erotic series is the most requested book by high-value detainees in Camp 7, which includes five men charged with plotting the 9/11 attack.

"I guess there's not much going on, these guys are going nowhere, so what the hell," Moran told the Huffington Post.

Moran, who is in favor of shutting down the detention camp, said he last visited Guantanamo in 2006, and that facilities at the camp had improved since then.

"In 2006, I didn't get the sense they had their act together like they do now, they anticipate every question that's going to be asked, the facilities look fairly clean, they're ready to show you everything that's been discussed outside the prison in terms of force-feeding, isolated confinement versus communal living, etc. and we were able to see the communal living," Moran said.

Regarding the detainees' reading habits, Lt. Col. Samuel House, a military spokesperson, refused to divulge much details saying, "We don't discuss our high-value detainees except in the most generic terms. Further, we do not discuss the assertions made by members of Congress."

Guantanamo has a detainee library, and according to Reuters, it is stacked with an eclectic collection of books, which include religious scriptures, Star Trek novels, mysteries penned by Agatha Christie, and self-help books.

All these books can be accessed by the 166 captives at Guantanamo, but sexual content in books is normally screened, the Reuters report said.

The three books in the “Fifty Shades of Grey” series have been 2012’s best-sellers, according to a Guardian report, and its publisher, Random House, has sold more than 70 million copies between March and December.

According to Jaclyn Friedman, author of "What You Really Really Want: The Smart Girl's Shame-Free Guide to Sex & Safety", who spoke to CNN, the series' success could be attributed to the fact that it is targeted at women.

"These stories focus on female desire and what's in it for the woman, and there's not a lot of that in mainstream culture," she said.