Google has expanded its online shopping and delivery services to more U.S. cities as it challenges Amazon.com. Chicago, Boston and Washington D.C. have been added to the Google Express service with more than 7 million people able to access its same-day delivery option, Google said.

Google is adding more stores and in August extended a mobile-advertising feature that shows what products are available nearby when users search for items.

Membership in Google Express costs $95 a year or $10 a month while consumers can also choose to pay as they go for $4.99 per eligible order. Same-day or overnight shipping for eligible items that cost more than $15 is free.