Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for delivering resources. The methods, systems, and apparatus include actions of based on measurements of amounts of a resource that are delivered from one or more supply outlets against amounts of value of electronic prepayments that have been authorized by corresponding users of mobile devices for the delivery of the resource at the one or more supply outlets, causing the one or more supply outlets to enable delivery of the resource in aggregate amounts that are not outside amounts of value of electronic prepayments that have been authorized by the corresponding users of mobile devices for the delivery of the resource.