But the prize comes with a caveat.
Wheldon, this year's Indy 500 champ, will start last in the field at Las Vegas and will only collect half of the money if he wins. IndyCar CEO Randy Bernard says the other $2.5 million will go to a fan chosen through a contest.
Series officials were trying to attract drivers from outside the series to compete at Vegas. Three expressed serious interest: NASCAR's Kasey Kahne, former CART and Formula 1 driver Alex Zanardi and extreme sports athlete Travis Pastrana. But deals for Kahne and Zanardi fell through, and Pastrana pulled out after breaking an ankle in late July.