XM Satellite Radio Holdings Inc. reported a wider first-quarter loss on Monday in spite of adding more subscribers.

XM, which is seeking regulatory approval for an acquisition by rival Sirius, said it lost $129.3 million, or 42 cents per share, compared with $122.4 million, or 40 cents per share, a year ago.

Analysts were expecting a loss of 39 cents a share on revenue of $313 million, according to Thomson Financial.

Washington-based XM said revenue rose 17 percent to $308 million from $264 million last year, but that fell short of the $313 million expected by Wall Street.

XM shares were trading 50 cents, or 4.2 percent, at $12.30 in afternoon trading.

As both XM and its merger partner Sirius Satellite Radio SIRI have done in the past, XM failed to provide 2008 guidance in its earnings report.

XM said that its subscriber base grew 9.33 million subscribers in March, up from 7.9 million a year earlier which represents an 18 percent increase.

In first quarter 2008 we delivered the largest number of new customers from the automotive channel in XM's history, marking the fourth consecutive quarter of record OEM gross additions, said President and CEO Nate Davis, in a prepared statement.

Total operating expenses rose 14 percent, with marketing costs up 24 percent from a year ago.

XM and Sirius announced plans to merge more than a year ago and have obtained their shareholders approval. The Justice Department signed off on the merger in June.

The merger still needs approval from the Federal Communications Commission, which has not indicated when it may issue a decision.

Sirius is set to report quarterly results after Monday's closing bell.