The kids who saw it don't have a clue whose car it is. This makes the true ownership of the car the biggest mystery about it. However, it's safe to assume that, as none of the Cul-de-Sac kids are of driving age, and because Eddy's Brother is out of town, it belongs to one of the parents (probably not Nazz's, Edd's, Jonny's, Kevin's, Rolf's or Eddy's, as they would have noticed). It is also possible that it belongs to somebody who lives outside the Cul-de-Sac.