Both stopped selling Kindles this year. Amazon reported similar growth for its devices. "Barnes & Noble is holding on to market share at the expense of profit," said Morningstar analyst Peter Wahlstrom. The investments to keep pace with rivals will make it hard for the Nook unit to turn a profit, he said. Lynch said Barnes & Noble has hung on to its 25-30 percent share of the U.S. e-books market. Nook accounts for 8.5 percent of total revenue. In August, early in the quarter, Barnes & Noble lowered prices on several Nook devices.