Google Inc. on Friday doubled the storage in its invitation-only email service, and said more increases were planned, as the giant search engine pulled ahead of rival Yahoo Inc. and continued to top Microsoft Corp. in the email storage race.

The Mountain View, Calif., company upped storage to 2 gigabytes for the free service, which remains in beta despite launching a year ago. With no indication on when Gmail would be generally available, Google said it would continue increasing storage capacity.

"Our plan is to continue growing your storage beyond 2GB by giving you more space as we are able," the company said on its website.

Google launched Gmail with 1GB of storage, prompting rivals to increase capacity in their free services. Yahoo currently offers 1GB, and Microsoft's Hotmail is up to 250 megabytes. When Google launched Gmail, Yahoo and Microsoft offered 4MB and 2MB, respectively.