United Parcel Service is following in the footsteps of its competitors by adding Saturday package pick up and delivery. UPS started testing the service last summer in a few markets, and will be adding 15 more this April. They hope to cover more than 4,700 cities and towns by the time the holiday shopping season kicks off this fall. Saturday delivery is a value-added service that can be added to UPS Air and UPS Worldwide Express services. UPS also offers a PDF with complete details including pricing here.
Both FedEx and the US Postal Service already offer delivery on Saturday, the later of which does not charge an extra fee for it.