WHITING, Ind. (AP) — BP estimates about 200 gas stations in northwest Indiana and the Chicago area and another 20 in the Milwaukee area were supplied with 2.1 million gallons of gasoline that has been recalled because it contained residue that can damage cars.

BP said in a release Wednesday it is continuing to contact retailers who may have received tainted gasoline that came from storage facilities in Whiting and Milwaukee.

The Indiana attorney general's office said Wednesday it is opening an investigation to ensure BP responds quickly to consumers' complaints about damaged vehicles. The investigation is in response to consumers calling the attorney general's office looking for claim process information or saying they were having trouble with their vehicles.

BP reports it has been contacted by 7,000 customers concerned about their gasoline purchases.