Before the April 29th launch of Grand Theft Auto, industry observers declared their intentions to use the sales as a way of determining the state of the ongoing battle between the Xbox 360 and the Playstation 3. After all, the Xbox 360 has the installed base advantage, with 9.9 million units sold since its November 2005 debut as compared to 4.1 million units of PS3 since its arrival November 2006, according to the market researchers at the NPD Group. What's more, savvy gamers would certainly know that Xbox 360 would be the exclusive home for Rockstar Games' planned-but-as-yet-unrevealed downloadable content. But the last five major Grand Theft Auto games either premiered on or remained exclusive to PS2 and PSP, and the bulk of those sales took place on PlayStation platforms. So could consumers' perception that GTA is somehow a PlayStation franchise give Sony the edge in unit sales, or at least enable the installed base-lagging PS3 to punch above its weight and take a greater share of GTA IV units sold than its market share would suggest?

We won't have a complete answer about how things shook out here in the United States until later this week, when the NPD Group releases its sales data for the month of April. But thanks to the kind folks at GameStop--North America's largest specialty videogame retailer--we've got a partial answer. According to sales information that GameStop has released exclusively to Level Up, 64 percent of the copies of Grand Theft Auto IV sold during the first week were for Xbox 360, while 36 percent were sold on PS3. Put another way, that's a roughly 2 to 1 sales advantage for Xbox 360.

So how does that split compare to the Xbox 360 and PS3's respective installed bases? As we said above, the NPD group reports that 9.9 million Xbox 360s and 4.1 million PS3s have been sold through the end of March 2008. (NOTE: these installed base figures do not include the month of April, so our back of the envelope calculations will be slightly off.) That's a total of 14 million units, of which 70.7 percent are Xbox 360 and 29.3 percent are PS3. So when we compare this to GameStop's split of GTA IV sales--64 percent on Xbox 360 and 36 percent on PS3--it's clear that GTA IV underperformed on Xbox 360 relative to Microsoft's pre-April installed base, while it exceeded expectations on PS3 relative to Sony's pre-April installed base.

We reached out to both Microsoft and Sony for comment. On the Microsoft side, when we asked Xbox director of product management Aaron Greenberg for his reaction to GameStop's first week's sales data, he replied via email:

I think many people have been surprised to see how well GTA IV is selling on Xbox 360 given the history of the franchise. These sales results add GTA IV to a long list of franchises that have switched over from Playstation to find a new home on Xbox 360 similar to what happened last year with titles like Madden and Guitar Hero. As you have covered on Level Up in the past, the majority of third party franchises are being developed first on our platform so they end up playing best on Xbox 360 and when you combine that with Xbox Live, we expect this trend to continue as more multiplatform releases hit the market. With that said, it is fantastic to hear that we beat PS3 two to one on Grand Theft Auto sales from a major retailer like GameStop.

In response to the same question, Playstation senior vice president of marketing Peter Dille during a phone conversation:

GameStop probably does a little bit better with the early adopter crowd. There's a larger installed base right now on Xbox 360 than on PS3. So it's not surprising that there's going to be more selling on Xbox 360 than PS3. Having said that, we're really excited about the ratio. If I had an installed base advantage of 3-1, I wouldn't be crowing too much about a 60-40 sales advantage. We think it's not as high as what GameStop's telling you, if you look at [the full picture on] the national level. They're outselling us, but not by that same margin, and it's because of their installed base lead. With an installed base lead that's close to 3-1, if you're bragging about a 60-40 software split, it's clear evidence that the Playstation 3 consumer is overindexing on GTA IV, and the Playstation brand loyalty that we've been talking about is bearing itself out in the marketplace as we speak.

We'll publish the full responses to our questions from both Greenberg and Dille later in the week.