Research company NPD Group, which tracks data from many electronics retailers, has released its sales numbers for May 2007, and it looks like Sirius Satellite Radio is maintaining its lead over XM at retail. Sirius held 55 percent of the satellite radio retail share for May, while XM pulled in 45 percent. This represents 21 consecutive months that Sirius has maintained a retail edge, according to NPD.

Year-over-year, Sirius sales are down 22 percent while XM is down 26 percent, and the entire sector is down 23 percent. However, the sector was down 24 percent on a year over year basis last month, so this actually represents an improvement from April to May. Meanwhile, XM has the edge in the month-over-month sales share comparison, as it is up 19 percent while Sirius is up only 17 percent.

It is worth noting that NPD does not track all retailers (Wal-Mart, some online sales, and sales directly by Sirius and XM are not in their numbers), but the study does include data from Best Buy, Circuit City, Radio Shack and others.

As for the status of the XM/Sirius merger, a letter signed by 72 members of the House of Representatives was recently sent to FCC Chairman Kevin Martin, Attorney General Alberto Gonzales, and Federal Trade Commission Chairman Deborah Platt Majoras opposing the idea.