According to the data released by The NPD Group figures for April, GTA IV has sold 1,85 million units on Xbox 360 and 1 million copies on PS3. However, GTA IV was followed in Top 10 best-selling games in the US by Mario Kart Wii which sold 1,120,000 units.

In May, GTA IV will have to face a serious and very different contender: the famous Wii Fit released by Nintendo in the US on May 19.

While GTA IV is an epic story about the adventures of an Eastern-European immigrant in Liberty City (a fictional town largely-based on New York), Wii Fit is build on totally different concept.

The Nintendo’s game combines the skills of a personal trainer and the fun one gets from playing video games, the newest Nintendo product measures the user's body mass index and sets players on various workout routines including strength training, aerobics, yoga, skiing, and snowboarding, all while sitting in front of their TV. The game was a blockbuster in Europe and in Japan, where it was already released.

GTA IV has a little advantage: it is available on both Xbox 360 and PS3, which means that it is a potential market of more than 16 million users (the combined installed-base of both gaming platform). Still, according to some analysts, Nintendo is on the verge to reach the 10-million units milestone in the US as early as next month.

So far, VGChartz.com, a gaming site that tracks games and consoles sales, said that Wii Fit has sold 650,000 units in its first day, and it could reach 1,2 million units in its first week.

If Wii Fit will manage to surpass the sales in GTA IV in May it remains to be seen, but one thing is sure: Wii Fit will sell better than Mario Kart Wii. Several retailers such as Amazon, Wal-Mart and Best Buy have already reported that Wii Fit is a sell-out two days after its official release.

Also, it will be interesting to see if Wii Fit will boost the sales of Nintendo Wii. In April, Nintendo’s gaming platform has sold
714, 000 units.