Sirius XM Radio (NASDAQ:SIRI) announced Wednesday its plan to offer buyers up to $550 million in aggregate senior notes, a move that comes as demand for its products continues to climb ahead of a year ago and profitability rises for the third consecutive quarter.

The debt maturing in 2018 is being offered through the New York-based company’s wholly owned subsidiary XM Satellite Radio.

XM plans to use the proceeds from the offering along with cash on hand to repurchase 11.25% notes maturing in 2013 via a cash tender offer and related consent solicitation.

If that falls through, the company intends to use the funds for general corporate purposes, which may include paying off debt.

The news comes as the company reported a 334,727 gain last quarter in subscribers, higher than the 102,295 new users in the fiscal 2009 third-quarter.

In the first nine months of the year, Sirius added nearly 1.1 million users, widely trumping a loss in the earlier period of 488,126 subscribers.

Total subscribers are now at a record 19.86 million, up more than 1.3 million from September 2009, and the company said it expects to hit 20.1 million by the end of the year.