(CNBC) — Newspapers, once reluctant to try to charge readers for access to their Web sites, have begun doing so in droves.

Across many of the developed economies of America, Europe and Asia, so-called pay walls are proliferating as publishers struggle to make up for dwindling revenue on their print products. Online advertising, once seen as the great hope for the future, has begun leveling off, which is accelerating the push for new Internet business models.

”Why now?” said Douglas McCabe, an analyst at Enders Analysis in London. ”The outlook for digital advertising for all but the very largest sites looks increasingly challenging. Therefore, it is critical that news services experiment with subscription models.”

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