LOS ANGELES (Reuters) - Four years after “Serial” put podcasts on the mainstream map with a twisty true crime murder story, Hollywood is rushing to embrace the audio format with everything from fictional thrillers to game shows.

70th Primetime Emmy Awards - Arrivals - Los Angeles, California, U.S., 17/09/2018 - Jessica Biel. REUTERS/Kyle Grillot - HP1EE9I01X0G2

At the same time, TV and movie producers are making their own podcasts, which are fast and relatively inexpensive to produce, in a search for the next breakout hit in a rapidly expanding crossover market.

Podcasts like “Dirty John” and “Homecoming” are already making their way to television with adaptations of “Dr. Death” and dozens of others underway.

“It’s the wild wild west for podcasts. The lines have gotten completely blurred,” said R.J. Cutler, producer of the “Nashville” TV series and “The World According to Dick Cheney” documentary. He recently launched his first podcast, the satirical “Oval Office Tapes.”

Portable and mostly free to download on smartphones, the number of Americans listening to podcasts has surged 35 percent in the last three years as content expands beyond radio shows on platforms, according to a study by consumer data company statista.com.

Some 44 percent of Americans say they have listened to a podcast at least once but it’s the 56 percent who have never listened that has attracted Endeavor Audio, a new unit of Hollywood talent and deal-making agency WME/Endeavor.

Endeavor Audio connects established producers with podcast makers and vice versa with a mission to develop, market and monetize the genre.

That includes formats like game shows and competitions, said Moses Soyoola, senior vice president of Endeavor Audio, which is working on a podcast series with television’s “Law & Order” franchise creator Dick Wolf.

Advertisers are taking note. Ad spending on podcasts are forecast to almost double to $659 million in 2020 from $313 million in 2017, according to a study in June by the Interactive Advertising Bureau.

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Soyoola said advertisers pay at least $20 for each 1,000 listeners a podcast gets. A premium podcast can charge more than $100 for every 1,000 listeners.

Paranormal mystery “Limetown” is a prime example of the potential. Season 2 of the podcast was released this month, a prequel novel is coming in November, and a “Limetown” TV show starring Jessica Biel is in development for Facebook Watch.

DON’T ALWAYS TRANSLATE

To be sure, successful podcasts don’t always translate into visual hits. The TV version of “Alex, Inc,” about a man who starts his own company, was canceled earlier this year after just one season. “Crimetown” is still in the early stages of development for television after being announced a year ago.

And the 2015 deal to adapt “Serial,” whose first season was downloaded globally some 240 million times according to the makers, is stuck in the development stage with “The Lego Movie” directors Phil Lord and Chris Miller.

Yet as players like Apple, YouTube and Facebook expand original content to compete with Netflix, Amazon Prime Video and traditional networks, a good track record in one medium is a safer bet than something untried.

“For the buyers, it gives them some comfort - the same as a best-seller book. It’s more likely to have an audience but you never know. It’s got to be well executed,” said podcast producer Cutler.

“Dirty John,” a tale of deception that has been downloaded more 32 million times according to its makers, makes its TV debut on Bravo on Nov. 25, starring Connie Britton.

Executive producer Alexandra Cunningham said the TV series would flesh out the characters heard but only imagined in the podcast and “explore questions that maybe you asked when you were finished (with the podcast).”

“Homecoming,” launched on Amazon Prime Video last week to glowing reviews, stars Julia Roberts in her first lead TV role. Executive producer Sam Esmail said “the throw-back thriller, based in characters” aspect of the podcast was what inspired him to turn it into a visual show.

Examples of other crossovers include the first scripted horror podcast, “The Horror of Dolores Roach,” adapted from an off-Broadway show, was launched in October. YouTube has ordered an animated series based on the podcast “Dumb People Town,” to be co-produced by “Arrested Development” TV star Will Arnett.