For the fourth consecutive quarter, Sirius (NASDAQ:SIRI) finds itself closing the gap with market share leader XM Satellite Radio (NASDAQ:XMSR). Heading into the seasonally spiked holiday quarter, Sirius was no slouch in generating 441,000 subscribers for the September quarter. It now has 5.1 million members. XM managed to sign up only 285,000 net new accounts, closing out the period with 7.2 million subscribers.

It may seem awfully convenient for Sirius to issue its press release only 23 minutes after XM did, but you have to hand it to Sirius here. XM may have more subscribers, but Sirius has been the real market leader lately.

The brand-new quarter should stretch Sirius' streak to five. The company is looking to land 1.2 million new listeners over the holidays. If XM sticks to its guidance, it will land between 500,000 to one million net new subscribers over the same three months.

Here is where XM bears watching. It's not too often that the larger company commands the smaller market cap, but XM is clearly the underdog, while Sirius is the one with all the momentum. That may change now that Oprah has taken over channel 156 on the XM dial, as the Oprah & Friends content blocks look to justify XM's $55 million investment in a three-year deal.

If Oprah's presence is able to reverse the trend -- no easy feat with the NFL and Howard Stern on Sirius' side -- XM shares might regain the market cap lead. But the Oprah effect hasn't really kicked in as it should have. Yes, her arrival came during the last week of the quarter, but Stern's buildup made Sirius the runaway favorite over the 2005 holiday season, weeks before "the king of all media" began his Sirius shows.

Perhaps the nature of the Oprah audience is to trickle in rather than create a stampede of early adopters, but there's no denying that this quarter will be the most important in XM's young tenure. If Oprah's tailwind can't help the company regain the lead in net additions over the holidays, it will be back to the drawing board for XM.

Satellite radio is an industry that deserves more market attention. Even in the traditionally sleepy third quarter, the duopoly combined to land 726,000 net new subscribers. Is the red ink turning you off? Do you have a beef with the way Sirius counts subs as they sit on the dealer lot? If so, you owe it to yourself to consider why your fears are likely overblown. Check out what executives had to say last month:

If the satellite-radio growth story rings hollow to you after that, your cynicism may warrant betting against one or both companies. I wouldn't recommend that. Until the net new subscribers become net new defections, satellite radio hasn't shown you all that it's got.

XM is an active Rule Breakers newsletter recommendation.

Longtime Fool contributor Rick Munarriz is a Sirius and XM subscriber. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. He does not own shares in any of the companies in this story. T he Fool has a disclosure policy.