Sirius XM (SIRI) surprised Wall Street on Tuesday by disclosing an unexpected fourth-quarter loss on weaker-than-expected sales, triggering a 4% slide in the satellite radio provider’s stock.

New York-based Sirius also issued cautious guidance that trailed analysts’ estimates.

The company said it lost $81.4 million, or 2 cents a share, last quarter, compared with a profit of $11.9 million, or break-even on a per-share basis, a year earlier. Analysts had called for break-even results.

Sirius, which renewed its contracts with both Howard Stern and the National Football League, said its revenue increased 8.8% to $735.9 million, slightly missing the Street’s view of $740 million.

Net subscribers grew last quarter by 328,789 to 20.2 million. The company grew its subscribers by 8% annually.

“SiriusXM's results in 2010 were exceptional, surpassing our guidance and achieving record revenues, adjusted EBITDA and free cash flow,” CEO Mel Karmazin said in a statement. “Our unparalleled content and the continuing improvements in the economy helped us attain a record-high subscriber base of 20.2 million.”

Sirius said it expects its 2011 sales to reach about $3 billion, which would slightly trail the Street’s view of $3.09 billion.

Hurt by the results and guidance, shares of Sirius slumped 4.92% to $1.74 ahead of the open.

"With the outlook for improving U.S. auto sales, declining capital expenditures and the expanded functionality coming with the launch of SiriusXM 2.0, we look forward to another year of growth and strong financial performance,” said Karmazin.

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