Mobile broadband customers have been warned to watch their monthly usage by a newly-published report.
Broadband Expert has pointed out that contract holders run the risk of racking up bills as high as £200 if they go as little as 1GB over monthly limits.
The broadband comparison site says that 1GB is the equivalent of downloading an episode of BBC motoring show Top Gear.
"Whilst many deals may appear to be very closely matched it is important to take excess charges into account, as there can be huge differences between one provider and another," said Broadband Expert's Commercial Director, Rob Webber.
He added: "Information on run on rates is not always easy to find and not obviously visible on most advertising."
According to Broadband Expert, O2 charge the most for exceeding data limits, with customers being billed 19.6p for every extra Mb.