Pandora announced Tuesday it has passed 200 million registered users. It took the company six years to gain its first 100 million registered users. The second 100 million arrived in fewer than two years.

Not all of registered users listen to Pandora on a regular basis, however. The company had 69.5 million listeners in March, which equates to roughly 35% of all registered users. That’s a slight drop from the 37.1 million monthly listeners, or 37% of registered users, who listened to Pandora had in July 2011 when it reached the 100 million milestone.

While Pandora is based in the United States and is well established in the market, the company now gets listeners from multiple countries. Pandora fully launched in Australia and New Zealand in December after quietly debuting in July. The two countries have a total population of roughly 27 million, or less than 9% of the United States’ population. Pandora declined to reveal how many registered users it has gained from Australia and New Zealand.

Pandora is benefitting from a shift to Internet radio in which more people are listening to Internet radio for longer periods of time. A new Arbitron report says the average U.S. consumer who listens to Internet radio weekly — these are very active users — listens for about 12 hours a week, up from 9 hours and 46 minutes per week in early 2012 and almost double the 6 hours and 13 minutes spent listening each week in early 2008. The average Pandora user listens for 20 hours per month. [Billboard.biz]