Sirius says it took 61% of total additions in Q3.

Satcaster Sirius on Wednesday (Oct. 4) revealed that it ended the third quarter on Sept. 30 with 5.1 million subscribers after adding 441,101 since July 1. That’s a 135% gain from the same time last year and a 23% increase over the third quarter gain in 2005 when it ended the quarter with 2,173,920 subscribers.

Sirius says it took 61% of the total satellite radio additions during Q3, falling in line with the on-going research by many Wall Street analysts.

Sirius reaffirmed its guidance that it would add another 1.2 million subscribers this quarter and end 2006 with a total of 6.3 million.

Rival satcaster XM also revealed Wednesday that it signed up more than 285,000 new net subscribers during Q3 for a total of 7.185 million subscribers. XM said the gains are within its earlier guidance and that it will end 2006 with 7.7 million to 8.2 million subscribers. XM has reduced its guidance twice in recent months and now says that analysts see its current projections as “a more realistic and achievable.”

D.C.-based XM also says its latest forecast “no longer included certain rental car fleets in its subscription total due to a new marketing program for 2007 model year vehicles.”