The cash-strapped U.S. Postal Service is moving aggressively this holiday season to start a premium service for the Internet shopper seeking the instant gratification of a store purchase: same-day delivery.

Teaming up with retailers, the post office will begin the service in San Francisco on Dec. 12. If things run smoothly, the program will quickly expand next year to cities such as Boston, Chicago and New York. It follows similar efforts by Amazon.com and Wal-Mart Stores.

The program seeks to build on the Postal Service's double-digit growth in package volume.

The retail market has seen a broader demographic shift in which Internet shopping has become a norm, and more people are moving from suburb to city, where driving can be less convenient.

The price is expected to be roughly $10.