The Ganassi cars late Thursday boosted the number of entries to 60. The speedway will accept others that were postmarked before the midnight Wednesday deadline.
Dixon, the 2003 series champion, has a five-point lead over Wheldon and Penske Racing's Helio Castroneves after finishing second at Homestead-Miami and St. Petersburg, Fla. The New Zealand driver has been runner-up in three straight races and four of the past five going back to last year.
"Obviously the second-place finishes are getting pretty old, but it shows the team definitely has a lot of speed across the board, not just on the ovals and mile-and- a-half configuration, but also on the road courses for the first attempt with the new car," Dixon said.
All of the Ganassi entries are Dallaras, the chassis used on 53 of the 60 entries.
There are two more races, in Japan on April 21 and at Kansas Speedway on April 29, before the series heads to Indianapolis for the race on May 27.
"I'm just looking forward to it," said Dixon, who will be trying for his fifth start at Indy. "Sometimes you just don't have the equipment. But at the moment we definitely have the equipment. Team Target (Ganassi) is very strong."
Wheldon, also trying for his fifth Indy start, won the race in 2005 and was fourth last year.
The other former winners entered this year are Castroneves (2001, 2002), Buddy Rice (2004) and defending champion Sam Hornish Jr.
"There's a lot of pressure coming into this race, and I like to drive with that," Wheldon said. "There's a lot of history and tradition involved.
"There's been a lot of great people that have won this race. There's also been great people that haven't won this race. So to have that opportunity and to be able to say that I've won it once I think makes me very hungry to do it again."
Among the other entries on Thursday were two cars by PDM Racing and three cars by Playa Del Racing, with no drivers listed by either team.
Practice will begin with the annual rookie orientation program May 6-7. The veterans will hit the track the next day, leading up to the first weekend of qualifications on May 12-13.