Streaming video service Netflix saw U.S. viewership of its original series jump from 57 percent of domestic subscribers in the first quarter to 72 percent in the third quarter. New shows and word-of-mouth likely helped spark interest in Netflix originals like “Orange Is the New Black.” Now, amid growing competition, Netflix hopes to replicate that success overseas with its upcoming high-budget original series, “Marco Polo,” which is set to make its international debut in December.

According to a new study by the research firm Centris Marketing Science, more subscribers are watching original content on Netflix. Millennials have the highest viewership of this type of programming, with 76 percent of 18- to 34-year-old subscribers watching Netflix original series in the third quarter. Adults ages 35 to 44 aren’t far behind with 71 percent tuning in.

Variety cites new shows, social media, word-of-mouth, and 31 Primetime Emmy nominations as reasons for growth.

Despite strong domestic viewership, Netflix is still cautious about its expansion overseas. After slow growth in European markets following the debut of the service in September, the company lost about a fifth of its market value, according to The New York Times.

Netflix is competing with the likes of HBO, which already has a strong international business. Analysts are worried that the rising licensing fees, especially as Netflix looks to buy more global rights to content, could put a financial strain on the company.

That doubt could dissipate if Netflix’s gamble on a new original series pays off. “Marco Polo” is a 10-episode extravaganza, filled with battles, martial arts, political intrigue, and sexual allure. The $90 million series was filmed in Italy, Kazakhstan, and Malaysia, with an international cast in hopes of attracting viewers across the world. The series will be available to stream in all of its markets on December 12.

Next year, the company plans to expand its markets to Australia and New Zealand. Meanwhile, HBO just announced a streaming deal in China. Netflix does not currently have any markets in Asia, but the company has not ruled out the possibility of expanding there in the future.