HBO executives have often said they value buzz about their programs just as much as ratings, figuring pop culture chatter can only help their mission to recruit new subscribers (and keep the ones they already have). That's why they don't sweat the relatively small audience for a show such as Girls: Almost every episode generates a ginormous amount of debate and discussion, while a random tweet from star Lena Dunham can launch a thousand blog posts (and that's just on Vulture!). In the case of Game of Thrones, however, HBO seems to have found itself the best of all mythical worlds: A buzz magnet that's presently hotter than seven hells (two words: Red Wedding) and a Nielsen hit whose ratings are growing with almost every episode.

So far this season, GoT is bringing in 4.9 million viewers with its 9 p.m. Sunday telecasts, up nearly 30 percent vs. last year's average of 3.8 million and basically double the 2.5 million who watched the show Sundays during its inaugural 2011 run. What's more, GoT is easily HBO's fastest-growing show since True Blood, the Alan Ball vampire thriller that, until GoT, ranked as HBO's top-rated series still in production.  And then there's this, as the chart below illustrates: GoT will end its third season Sunday as the most popular series on HBO since the Adrianna-whacking fifth season of The Sopranos.

(Note: This data, provided by HBO, cuts off shows that's season highs were below Treme's, including Enlightened and How to Make It in America.)

Now, before sounding off in the comments, the 13.6 million audience tally for GoT cited in the chart is not a typo. As noted above, the show is averaging around 5 million viewers for its 9 p.m. Sunday play on HBO. But like most HBO series — as well as a slew of other basic and pay cable shows — that first telecast reps just a small portion of the eventual audience for each episode. For example, the instant encore of GoT that airs at 11 p.m. Sunday can add more than a million more viewers to the tally. The number goes up by about another third when everyone who recorded the show on DVR finally plays it back. The countless repeats on HBO and its so-called "multiplex" channels (HBO2, HBO Latino) boost viewership by about 15 percent, while folks who watch an episode on demand add a similar amount to the final tally. Finally, those who like their GoT carnage on the streaming app HBO GO tack on another 6 percent. Add it all up, and GoT nearly triples its initial audience, ending up with the aforementioned 13.6 million total viewers. (And in case you were curious: The show's overall audience is 57 percent male and 43 percent female, according to HBO.) It's worth noting here that, while GoT has passed True Blood and is drawing more viewers than the final seasons of The Sopranos, new technology makes it tough to compare tune-in figures. HBO GO had only been around for a few months when True Blood hit its 2010 peak,cheapest music cds, and it didn't even exist when Tony Soprano ruled HBO. Video on demand also wasn't as widely available as it is now back during the era of The Sopranos, nor were DVRs. That makes the numbers for The Sopranos all the more impressive: As big as GoT is, it's nowhere near the monster hit its Sunday predecessor was (nor has it amassed anywhere near the Emmy haul of David Chase's show). At least not yet.

The blizzard of attention Sunday's Red Wedding episode drew may very well convince a lot of folks who haven't yet gotten into the show to finally catch up. The bump might not present itself in the ratings for this week's finale, but instead could come when the show returns next spring and newbies have had a chance to watch past episodes. While most (but hardly all) broadcast shows tend to fade after their third or fourth seasons, cable breeds late bloomers. AMC's Breaking Bad grew at a modest clip during its first four seasons, but after all episodes landed on Netflix, the show's ratings among adults under 50 exploded by 65 percent in season five. FX's It's Always Sunny in Philadelphia and Archer have experienced similar ratings surges after their third seasons. True Blood also went through a big growth spurt on HBO, though its path to blockbuster status was a bit quicker than GoT's. True Blood more than doubled its Sunday audience between its first and second seasons,dvd series tv, while GoT took three seasons to accomplish a similar feat. Since we're not part warg, we have no idea if GoT will boast even more viewers in season four. But consider this: The show has already added nearly a million viewers just during the course of the current season, debuting with 4.4 million on March 31 and reaching as high as 5.5 million for an episode last month. Like Daenerys's dragons, Game of Thrones seems likely to get a whole lot bigger.