In the first half of 2015, sales at Penguin Random House rose 16.2%, to 1.70 billion euros, while earnings increased 30.2%. The numbers, which indicate changes in comparison to the same period in 2014, were reported by parent company Bertelsmann this morning.

Operating EBITDA at PRH hit 207 million euros, up from 159 million euros in last year’s first six months. Bertelsmann attributed much of the increase to the positive effects of currency fluctuations, but also noted that the company had a large number of bestsellers in all of its worldwide operations, topped by The Girl on the Train which has sold more than 4.5 million copies.

In remarks made in Germany during the presentation of results, Bertelsmann chief executive Thomas Rabe said the company would consider upping its stake in PRH, which now stands at 53%, with Pearson, the former parent company of Penguin, owning 47%. Under the merger agreement Bertelsmann and Pearson are committed to hold onto their respective stakes in PRH for three years. That period, though, is expiring soon.

Rabe’s comments came as little surprise, since Bertelsmann has been much more proactive in book publishing than Pearson. Indeed, Reuters quoted Rabe saying that "publishing has always been at the heart of Bertelsmann and it always will be. We could imagine raising our stake in Penguin Random house in steps."

In his letter to employees, PRH CEO Markus Dohle said that even in his “most optimistic moments I could not have foreseen the publishing successes we have been enjoying this year.” In addition to Train, he pointed to Grey, The Life-Changing Magic of Tidying Up, What Pet Should I Get?, and Between the World and Me as notable first half hits.

Outside of the U.S., Bertelsmann noted that Penguin Random House Grupo Editorial had an “excellent performance” in Latin America and double-digit growth in e-book sales. The latter offset problems in the Spanish book market. The company also made progress in integrating the Spanish and Portuguese-language publishing activities of Santillana Ediciones Generales, which was acquired last year.