Apple’s podcast app may be where about 60% of podcast listening takes place but what does that mean in terms of actual users? A new estimate from the Silicon Valley venture capital firm Andreessen Horowitz pegs the number at 27 million monthly active users in the U.S. for Apple Podcasts. While that’s a sizable number, the firm says it’s still “relatively small” compared to the 900 million people using iPhones worldwide.

Apple’s biggest advantage is the podcast app comes pre-installed on phones, the report says, since the company currently doesn’t monetize podcasting at all. In the face of growing competition from other apps offering podcasts, Andreessen Horowitz also casts doubt on whether Apple will be remain dominant. “From our research, users seldom feel passionately — either positively or negatively — about the podcast app they’re using. This suggests that the audio content itself is the core element users are engaging with, and since the content is the same on all apps, users don’t feel particular affinity to any one listening app,” it says.

Andreessen Horowitz notes that Spotify already has, by its estimate, 9% of the podcast listening market while apps like iHeartRadio with 120 million registered users and Pandora with 66 million monthly active users are benefiting from the ability to cross-promote podcasts to a large existing user base. It also notes that Google Podcasts may yet be a significant factor in global podcast listening.

There’s also a third tier of what the Andreessen Horowitz describes as the “long-tail” listening apps, a list that includes apps such as CastBox, Stitcher, Pocket Casts and Breaker. They are predominantly competing on the basis of better user-facing features such as improved discovery, search, and social capabilities.

Despite all the places to listen to podcasts, analysts say actual money-making remains in its infancy. “The current state of monetization in podcasting mirrors the early internet: revenue lags behind attention,” the report says. “Despite double-digit percent growth in podcast advertising over the last few years, podcasts are still in a very nascent, disjointed stage of monetization today.”

Although marketers have anecdotally said podcasts advertising is effective, Andreessen Horowitz believes the format remains “manual and tedious” for buyers—especially when compared to other digital media. It also said Nielsen research has shown that podcasts monetize at only a $0.01 per listener hour, on average. That’s ten-times less than radio or television, and nearly 25-times less than other digital media.

“Based on our conversations, lag in monetization isn’t due to lack of efficacy of ads,” it says. Instead it blames the inability to monetize directly on the dominant platform—Apple Podcasts—as the biggest culprit. It says marketers are also only interested in buying ads on the shows with the most listeners, leaving a large number of producers unable to monetize their content. Andreessen Horowitz says there’s also a continued “lack of clarity” around actual listener numbers and detailed listener demographic data is also not available. “There’s also a lack of sophisticated targeting tools on par with what Facebook and other digital platforms offer advertisers,” it says.