The deal must still be approved by regulators in the United States and Europe. But if it is completed and further consolidation occurs, midsize companies in the crowded field of mass-market book publishing might find it especially difficult to compete, because the bigger publishers will be able to extract favorable terms from customers or to invest in digital operations. Small publishers with a niche focus and loyal groups of authors and readers might manage to remain independent, said Douglas McCabe, an analyst at Enders Analysis in London.

The combination announced Monday is the first major publishing industry merger since Bertelsmann paid more than $1 billion for Random House in 1998. James L. McQuivey, a media analyst at Forrester Research, said that as far as gaining regulatory approval, Random House and Penguin should benefit from being the first of the major publishers to merge. “It’s easier to argue that the industry going from six to five publishing houses won’t change the market, than arguing that going from five to four players won’t impact competition,” he said.

“Regulators generally understand that these companies aren’t just competing with each other, they’re competing with a very changed marketplace,” he added.

Mr. McCabe said he thought the deal would be approved, possibly with some concessions.

“Authors will be very interested in this, so the process could be more drawn out than they hope,” he said. “This is not a merger of two widget makers that nobody will notice.”

One person briefed on the talks said Pearson had considered all options for Penguin, including an outright sale. But a sale would have been difficult, this person said, because it would have prompted prohibitively high capital gains taxes in the United States.

Under the agreement, Markus Dohle of Random House will be chief executive of the new entity, which would have annual revenue of about $3.8 billion. In a phone interview Mr. Dohle said he expected Penguin Random House to be able to cut costs in areas like supply chain distribution. “The goal of the new company is not about cost efficiency, but about efficiency in better services,” he said. “But together we have a bigger physical footprint so of course that helps get the physical cost-per-copy down.”

Marjorie Scardino, chief executive of Pearson, also said that cost-saving synergies were not the primary motivation for the deal. She said the combination would help Penguin Random House “invest in books and in new ways of deploying them.” This could include digital platforms for selling books directly to consumers, she said, as well as new digital formats.