The vast majority of US newspapers have implemented digital subscriptions or "paywalls" to cope with the decline in print, a survey showed Monday.

The survey by the American Press Institute showed 77 of the 98 US newspapers with circulation above 50,000 used some type of online subscription model.

That is a major shift from 2010, when only six newspapers used digital subscriptions, the survey found.

The "paywall" model varies at the publications, the survey found:  62 newspapers used a "metered" system that allows visitors to read a specified number of articles for free, while 12 used a "freemium" model that offers some kinds of content for free and others only to subscribers.

Just three of the newspapers used a "hard" paywall where subscriptions are required for the vast majority of content.

The report said it's not clear if the paywalls will allow newspaper to compensate for the loss of print readers and advertising revenues.

"The potential revenue generated by digital subscriptions is still murky at best," API research fellow Alex Williams said in the report.

"In the first year or two after launching a digital subscription plan, a publisher captures a large share of people who were already willing to pay for digital access. But going forward each new subscriber must actively be won, converted, persuaded. The prospects for long-term growth rates in digital subscription revenue are unclear."

The survey showed the newspapers charged an average of $3.11 a week for a digital-only subscription and $3.29 for a digital subscription plus a Sunday print newspaper.