With Internet usage spiking, Comcast Corp. will eliminate its monthly 250-gigabyte cap for Xfinity Internet subscribers but charge additional $10 fees for users who exceed 300 gigabytes.

The 300-gigabyte limit could be used to videoconference on Skype for 225 hours, or watch more than 100 hours of Netflix movies.

Final details of the new plan were not available on Thursday because they have not been developed, company officials said in a conference call. The nation's largest broadband company with 18 million Internet subscribers will experiment with two new usage-consumption models in markets around the country before determining the best option for it and consumers.

The changes, Comcast said, were not likely to impact many subscribers because the median monthly consumption for an Xfinity Internet customer is eight to 10 gigabytes — well below the 300-gigabyte threshold. Users who exceed 300 gigabytes could be charged $10 for each additional 50 gigabytes.

David Cohen, Comcast executive vice president, said the new policy eliminates a Comcast cap on Internet usage. Under its previous policy, the company could cancel an Xfinity user's Internet if they exceeded 250 gigabytes a month and ignored warnings to curb usage.

Free Press policy director Joel Kelsey, a frequent Comcast critic, said he believed the usage limits were unjustified and the additional charges punitive. These Comcast limits, he said, seemed designed to "thwart competition" by making people think twice about viewing online video. Free Press is a nonprofit advocacy group.

The new policy was announced during a week when Comcast disclosed it was officially launching its Skype service on TV, which will count toward Internet consumption. Comcast also has faced recent criticism for not counting toward monthly Internet consumption its cable-TV service streamed through Xbox 360 consoles. Critics say the service uses the Internet and should be counted. Comcast says the streaming is done on its private network and doesn't need to be counted.

It was time to reset the consumption policy, Cohen said. "As times change, we change," he said. "The vast, vast majority of our customers will be unaffected by this announcement."

Contact Bob Fernandez at 215-854-5897 or bob.fernandez@phillynews.com.