A new report issued by the Audio Publishers Association found that 2016 was another good year for audiobooks. The findings show double-digit growth for both audiobook sales and title output.

Total sales rose 18.2% over 2015, to an estimated $2.1 billion, while unit sales did even better. According to the report, unit sales rose 33.9%, to 89.5 million. Sales are based on reports from about 20 audiobook publishers. The APA then extrapolates from those figures, to derive an estimate for the entire market. The title output from reporting companies was 50,937 in 2016, a 43.1% increase over 2015.

The sales increase was driven by digital downloads, which accounted for 82.4% of sales. In 2015, digital downloads accounted for 76.8% of sales. Sales of physical audio, meanwhile, declined. Last year, sales of physical audio represented 16.2% of total audio sales, down from 21.8% in 2015. While sales of physical audio dropped again last year, the rate of decline has slowed slightly.

A study by Edison Research found that 24% of Americans listened to at least one audiobook in 2016, an increase of 22% over 2015. Other demographic findings showed that almost half of audio listeners are under the age of 35, and that audiobook listeners either read or listened to an average of 15 books in the last year.

Smartphones increased in popularity as the device of choice for audiobook listening, capturing 29% of the audiobook audience. According to the survey, the top reasons people chose audiobooks is that they can do other things while listening, and the portability of the content. The most popular genres last year were mysteries/thrillers/suspense, science fiction/fantasy and romance

“It’s another banner year for audiobooks,” said Anthony Goff, senior v-p, publisher at Hachette Audio and research committee chair for the APA. “It has been exhilarating for everyone involved in audio to see such healthy growth maintained, year in and year out." He added: "Learning more about audiobook listeners by digging deeper into the metrics of consumer behavior is one of the key ways we can help that growth continue.”