Online music streaming service Pandora (P) has 200 million registered users in the U.S., the company announced today. It took the company six years to hit 100 million and it has doubled that number in under two years.

"We started this company to help people discover and enjoy music they love, and to help artists reach and grow their audiences. Only in our wildest dreams did we imagine what it would become," Tim Westergren, founder of Pandora, was quoted in the company press release as saying.

The company launched in the summer of 2005 and achieved 100 million registered users in July 2011.

Pandora says it streams 200 million songs before 10 a.m. everyday and that more than 140 million listeners have streamed Pandora from a mobile device. The company streamed 1 million unique songs last month and the company says "the vast majority of that music got no other terrestrial radio airplay."

Pandora said "tens of millions" of people use the service every month.

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