Sirius XM Radio Inc shares topped $1 a share on Wednesday, vaulting the critical threshold for the first time in 17 months, amid improved sentiment about the pay-radio company's future.

The stock, up 8.5 percent to $1.04 in morning trading, has improved ten-fold since January 2009, when concerns about looming debt payments pushed it to the brink of bankruptcy.

It last was above $1 in September 2008.

Staying above $1 removes the threat that the company, whose market cap is about $3.7 billion, might face delisting by Nasdaq. Sirius XM Chief Executive Mel Karmazin told Reuters in November that he was confident there would be no delisting.

Crossing $1 might also make the stock more palatable to mutual funds that would shy away from a company whose shares trade under $1.

Sirius has bolstered its books following an investment last year from John Malone's Liberty Media that gave Malone a 40 percent equity stake in the company. Last month, Sirius said it will report more than $100 million in free cash flow for 2009, after reporting negative free cash flow of $552 million in 2008.

Analysts have attributed the stock's comeback to improved outlook for sales on the auto sector, where Sirius gets most of its new subscribers, and improved percentage of customers who convert to paying customers once trials expire.

(Reporting by Franklin Paul, editing by Dave Zimmerman)