The nation's two big satellite radio companies continued their frenetic pace Tuesday, signing a pair of partnership deals.

XM Satellite Radio

(XMSR)

, the biggest pay radio company, with more than 2.5 million subscribers at last count, said it arranged to have its radios available at National Car Rental and Alamo Rent A Car.

Meanwhile, headline-grabbing rival

Sirius

(SIRI) - Get Report

signed an agreement to provide its users with real-time traffic data via the

Navteq

(NVT) - Get Report

network.

Washington, D.C.-based XM said National and Alamo customers can receive XM Radio for no additional charge on all 2005 model Chevrolet Cobalts, Pontiac G6s and Buick LaCrosses in the two brands' fleets. The two rental brands also are offering XM for no extra charge on select 2005 Chevrolet Monte Carlos, Chevrolet Impalas and Pontiac Bonnevilles.

New York-based Sirius, which has rocketed in heavy volume in recent weeks after the company lured shock jock Howard Stern and media honcho Mel Karmazin, said its traffic service will initially cover 30 markets and is expected to expand to over 50 markets. Sirius said its "automotive and retail partners have shown a high level of interest in the new service, and plan to offer it as a product upgrade for their upcoming navigational systems."

Sales of the traffic suite could potentially add a much-needed new revenue stream for Sirius, which has impressed investors by bringing aboard new programming but which has yet to show how it will pay for it all. The company said Tuesday that the traffic feed is "expected to provide an additional revenue stream for Sirius, which the company believes will have a positive effect on its average revenue per user when implemented."

Shares of both XM and Sirius have risen sharply over the last two years as investors sign on to their heady growth plans. Reflecting their stock market success, both companies were added this month to the Nasdaq 100 index, which tracks the best-capitalized nonfinancial companies on the tech-heavy Nasdaq market. The companies have become fierce rivals, battling both for customers and for headlines, as expressed last week by the one-upmanship in the publicity surrounding their respective agreements with

Toyota

(TM) - Get Report

.

Early Tuesday, Sirius rose 8 cents to $8.12, and XM added 23 cents to $39.