The video service is known for original movies and shows, but at the same time it doesn’t disclose what percentage of videos on Prime are uploaded. Photo: Debarchan Chatterjee/Zuma Press

When Walter Wilson, a construction worker from North Carolina, sat down to watch the blockbuster “Avengers: Endgame” on Amazon Prime Video, he ended up seeing something very different: a 2007 documentary, also titled “Endgame,” directed by far-right talk show host Alex Jones.

Mr. Jones’s videos have been banned from many mainstream sites like Apple Inc.’s iTunes and Facebook for promoting outlandish conspiracy theories. “Endgame” purported to document a clandestine organization of bankers and politicians bent on establishing a “blueprint for global enslavement.”

Its availability on Amazon.com Inc.’s streaming service highlighted a fact not widely known among subscribers: The e-commerce giant accepts nonprofessional and questionable content to offer a video library that in Amazon’s style can dominate the competition through sheer volume.

While the video service is known for original movies and shows that have won Oscars and Emmys—such as “Manchester By the Sea” and “Transparent”—the site also carries thousands of conspiracy-theory videos, amateur productions and short instructional clips. Similar to Alphabet Inc.’s YouTube, some videos are uploaded by individuals who made them or by others owning the rights to the content. Others Amazon bought in bulk as part of vast libraries of amateur content.

Wide Selection

The number of titles in Amazon’s library outpaces rival streaming-video providers and helps the service to attract customers.

Number of distinct titles by service,
December 2019

65,504 titles

Amazon

7,177

66% of Amazon uploads are user uploaded.

Netflix

6,564

Hotstar

5,440

Hulu

Q4 2019 U.S. customer base by service

1,312

HBO Go

1,039

Crunchyroll

Amazon

42.2

Netflix

1,002

Starz Play

61.3

Disney+

916

Showtime Anytime

759

Disney+

Britbox

696

23.2 million

Apple TV+

AcornTV

570

33.6

CBS All Access

553

Hulu*

31.8

Max Go

358

Apple TV+

11

65,504 titles

Amazon

7,177

66% of Amazon uploads are user uploaded.

Netflix

6,564

Hotstar

Q4 2019 U.S. customer base by service

5,440

Hulu

1,312

HBO Go

1,039

Crunchyroll

Amazon

1,002

Starz Play

42.2

Netflix

61.3 million

916

Disney+

759

Showtime Anytime

696

Britbox

Apple TV+

33.6

AcornTV

570

Hulu*

553

CBS All Access

31.8

Disney+

358

Max Go

23.2

11

Apple TV+

65,504 titles

Amazon

7,177

66% are user uploaded

Netflix

6,564

Hotstar

5,440

Hulu

Q4 2019 U.S. customer base by service

1,312

HBO Go

1,039

Crunchyroll

1,002

Starz Play

Amazon

42.2

916

Disney+

Netflix

61.3 million

759

Showtime Anytime

696

Britbox

Apple TV+

AcornTV

570

33.6

553

CBS All Access

Hulu*

358

Max Go

31.8

Disney+

23.2

11

Apple TV+

Amazon

65,504 titles

66% are user uploaded

Netflix

Starz Play

AcornTV

7,177

1,002

570

Hotstar

Disney+

CBS All Access

6,564

916

553

Showtime

Anytime

Hulu

Max Go

5,440

358

759

Britbox

HBO Go

Apple TV+

696

11

1,312

Crunchyroll

1,039

Q4 2019 U.S. customer base by service

Amazon

42.2

Netflix

61.3 million

Apple TV+

33.6

Hulu*

31.8

Disney+

23.2

*Includes Hulu TV

Source: Ampere Analysis

An Amazon spokeswoman says the company has sought a broad selection of content, including videos from award winners and independent producers.

“We continuously review and monitor titles to ensure that they are in accordance with our policies and guidelines,” she said. “If content is identified as not meeting those standards, it is immediately removed.”

YouTube, a self-avowed creature of user-generated video, also has faced the challenge of policing objectionable content on its site.

Mr. Wilson and other Prime Video subscribers said they have enjoyed some of the non-mainstream programming they have found on the service, and some independent producers call it a valuable outlet to reach a broad audience.

Amazon Prime members get unlimited viewing of videos, as well as free shipping for physical goods, at a cost of $119 a year.

After inquiries from The Wall Street Journal, Amazon took down “Endgame” and two other videos from Mr. Jones—all self-uploaded, according to the company—citing violations of company policy. The company’s content policy focuses on issues pertaining to the sexually explicit, violence and copyright infringement, but it gives Amazon leeway to disallow anything it deems inappropriate.

Mr. Jones’s company, Infowars, didn’t respond to requests for comment.

Amazon boasts that its library of more than 70,000 movies, television shows and videos is several times bigger than top rivals like Netflix Inc. and Walt Disney Co.’s Hulu.

Amazon executives say that to bulk up quickly, especially in foreign countries, the company has encouraged people with rights to videos to self upload through an automatic system without first negotiating licensing deals with studios and other major companies, which can be time-consuming. Neither Netflix nor Hulu has such a self-upload feature.

Some well-known movies from years ago, such as “Thelma and Louise” and “Silence of the Lambs,” were uploaded by movie studios that way, Amazon says.

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So was plenty of amateur content—some of it with misleading titles. Amazon pays uploaders based on video views, creating incentive to use titles that are attention-grabbing. For example, a 12-minute user-uploaded clip of a videogame was titled “Clip: Elsa from Frozen Cooking Show Game.”

Amazon’s approach to video echoes that of the company’s core e-commerce business. There, third-party sellers now account for a majority of sales after Amazon spent years building a reputation as a reliable direct seller of books and other items.

But such openness invites risk. The Journal last year reported that thousands of consumer products listed by third parties on Amazon were deceptively labeled or had been deemed unsafe or banned by regulators. The company, which took down some of those listings after the Journal’s reporting, said it is investing billions to root out unsafe and counterfeit products.

In the case of self-uploaded videos, the company employs an artificial-intelligence tool to detect obvious violations of its terms of service, such as pornography or copyright infringement. Humans also review user comments for mentions of anything potentially offensive.

The company doesn’t disclose what percentage of videos on Prime are uploaded and unlike YouTube doesn’t label user-generated content on the site. But former Prime Video executives say such content is now a majority of videos. A December analysis by Ampere Analysis found about 22,500 movies and TV shows on the service were professionally made, while more than 43,000 were user-uploaded.

Conspiracy-theory videos and a range of amateur clips can be found on the site. Photo: Amazon

YouTube, the biggest site for user-generated videos, identifies the account that uploaded a given video, whether it is a Hollywood studio or an average person.

Amazon Prime Video has become an important distributor for Chris Emery, the producer of “A Noble Lie: Oklahoma City 1995,” a documentary that argues Oklahoma City bomber Timothy McVeigh may have been persuaded to blow up the federal building through government-sponsored mind control. Netflix removed the documentary in 2012 with no explanation, and sales for the DVD had plummeted by 2015.

Getting the movie on Prime Video “has really launched us world-wide,” Mr. Emery said, adding the movie is watched thousands of times a month in markets as far-flung as the Philippines and Russia.

To get a sense of what else on Amazon’s vast platform was getting noticed by viewers, the Journal analyzed the metadata associated with 50,000 Amazon Prime videos of all sorts. Controversial content drew a lot of response from viewers.

For example, “Dreams from My Real Father,” which falsely reports that Barack Obama’s biological father was a Communist Party member and CIA agent, ranked No. 8 among the most-reviewed features in the Special Interest category. “The Enemies Within,” about how certain Democratic members of Congress purportedly collude with the Muslim Brotherhood and other radical organizations, is No. 10. Both videos received as many comments as several historical miniseries by documentarian Ken Burns.

The Journal also ranked the most-prolific uploaders on the site and in their content found many innocuous examples of amateur video.

Jasmina Susak has posted more than 200 art-instruction videos, including “Clip: Drawing Chuck Norris” and “Clip: Time Lapse Drawing McDonald’s Menu.” Another prolific user, a Bible teacher named Mike Mazzalongo, said he has uploaded about 1,000 videos of his sermons on sinning and the power of prayer. Both users have more videos on Prime Video than any major Hollywood studio except Viacom Inc.’s Paramount Pictures.

More than 400,000 minutes of Mr. Mazzalongo’s videos were streamed over four weeks in November and December, said Hal Greenwood, the technology manager at BibleTalk.tv, the company behind the videos. The platform broadened their reach, he said, with the added benefit of bringing in about $500 in revenue.

Appearing on Amazon can also confer a level of credibility that sites like YouTube cannot. The Producers Guild of America, a key professional association, recognizes Amazon Prime as a streaming platform that can help a producer to qualify for membership—though at the same time its policy states that “direct-to-consumer or noncurated distribution platforms cannot be used to qualify a film for distribution.” Other means recognized by the guild include Hulu, Netflix, theatrical release, distribution through mainstream cable or appearances at a handful of major film festivals.

Mr. Wilson said he proceeded to continue watching “Endgame,” the Alex Jones documentary, and found it persuasive. “I do have concerns about the so-called shadow organizations and New World Order, because somebody, somewhere, is pulling the strings,” the 67-year-old construction worker said.

Other viewers said they appreciated the seemingly limitless number of offerings. Bethany Wickham, a 38-year-old photographer in Southern California, said she loves watching obscure crime documentaries on Amazon, even though some are extremely shoddy.

“There might be that diamond in the rough,” Ms. Wickham said.

Write to Erich Schwartzel at erich.schwartzel@wsj.com, Shane Shifflett at Shane.Shifflett@wsj.com and Alexandra Berzon at alexandra.berzon@wsj.com

Corrections & Amplifications
Amazon makes payments to video uploaders that is based on views for their clips. An earlier version of this article incorrectly said the company sells ads on the Prime Video site—a practice it has discontinued—with a portion of the ad revenue going to uploaders. (Jan. 23, 2020)

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