According to a number of recent reports — including earnings reports from large publishers and independent research by industry specialists — an explosion in recent audiobook sales is helping to keep publishing out of the red.

In particular, sales of downloadable audiobooks have grown by 34% percent across all categories and 38.9% within the adult books category, according to data from the Audio Publishers Association and the Association of American Publishers. Physical audio declined a slight 5.7% over 2014, when overall sales boomed.

In total, based on information provided by the firm Management Practice (to the Audio Publishers Association), audiobook sales reached $1.77 billion over the last year. It amounts to a 20.7% increase over 2014, when sales had expanded by more than 20% over the previous year.

The number of published audiobook titles increased dramatically in 2015, too, with an additional 9,630 titles being published over 2014. The total number of audiobook titles published came to 35,574, which, according to the APA, amounts to “an increase of 29,374 more audiobook titles published per year from only five years ago.”

And, according to recent research, the audiobook market is dominated by adult fiction, which accounts for more than 76.3% of total sales:

Sales for adult titles continue to dominate the market and account for 90.4% of overall audiobook sales. Fiction continues to represent the vast majority of audiobooks sold with roughly 76.3% of audios being fiction vs. 23.7% non-fiction. The unabridged format continues to predominate with 96.3% of audios sold being in this format.

Recent earning reports for the quarter ending on March 31, 2016 confirmed the strength of digital audio downloads across the industry — if we take the word of CEOs and parent company representatives, audiobook downloads are keeping digital publishing departments afloat. Michael Pietsch, CEO of Hachette Book Group, cited “lower unearned advances and continued strong sales of HBG’s downloadable audio” as important factors determining the publisher’s earnings outcome. And Publisher’s Weekly explained that Simon & Schuster’s revenue stayed out of the negative because “[s]ales of digital audio were up by double digits in the quarter and [Simon & Schuster] continues to add more titles to the format, including doing more digital-only audiobooks.”

The short-term rise in audiobook sales comes as publishers deal with an industry-wide decline in ebook sales. In the quarter ending on March 31, HarperCollins reported a 23% decline in ebook revenue. And both Simon & Schuster and Houghton Mifflin Harcourt posted flat or falling ebook sales, which largely accounted for lackluster quarterly earnings.

The underlying reason behind the precipitous increase in audiobook sales over two years is unclear, but it’s worth noting that the format brings together decades of “talent” — favorite voice actors, like Dick Hill — to tablets and mobile phones. This has the effect of bridging separate generations of readers, including young readers who download audiobooks on their phones and older readers who once relied on the public library system for books on tape or CD. And the industry has been quick to marshal the familiarity of celebrity voices to read popular publication. Harper Lee’s Go Set a Watchman, a hit novel, was read by actress Reese Witherspoon.

Will audiobook sales slow in a sluggish 2016? In some cases, audiobook versions are registering three or four times the sales number of the original work; they are, in effect, replacing the text version as the primary version of the “book.” Given the proliferation of reading devices and the decreasing costs of production, there is little reason to believe sales will slow, even as ebook sales stagnate.

Small, independent publishers will likely turn to audiobooks for additional revenue. We wrote yesterday about the increase in market share for books by self-publishers and small publishers; both are finding encouragement in the creation of their own audiobooks. The vast majority of audiobook sales is now restricted to the “Big Four” and Amazon’s Audible.