Trainor, of the DEA, said corner groups often buy heroin in quantities as small as a few ounces to resell. He said that Mexican cartels are the main source of large shipments to the United States, although he and other officials were more circumspect about how drugs trickle out to the corners. Trainor said cartels sell heroin for about $60,000 per kilogram (2.2 pounds), about half the price of what producers in South Asian countries, such as Afghanistan or Thailand, had charged when they were dominant suppliers.