This month's figures show Guardian News & Media's operation in the lead for unique users with a closely-knit chasing pack of second-placed Times Online, third-placed Sun Online and fourth-placed Telegraph.co.uk.
Guardian Unlimited registered a total of 15.1m unique users during the whole of March and 147m page impressions.
News International's Times Online registered 8m unique users and 58m page impressions.
Fellow Rupert Murdoch-owned site Sun Online registered 7.8m unique users and a table-topping 151m page impressions.
Telegraph.co.uk registered 7.4m unique users and 70m page impressions.
The ABC figures provide a common benchmark for web traffic, based on reporting standards to which the companies engaged by publishers to measure their figures, such as Hitwise and Web Side Story, must adhere.
They include users from outside the UK, which contributes to Guardian Unlimited's commanding lead given the site's popularity outside the UK, particularly in the US.
Newspaper groups have also issued their own figures, leading to arguments within the industry about unfair comparisons.
Telegraph.co.uk recently upset rivals by running an advertising campaign claiming it was the UK's most visited quality newspaper website, using statistics from Hitwise for a three-month period.
The claim was allowed to stand by the advertising watchdog, the Advertising Standards Authority, which investigated after a complaint from an unknown source. The ASA said the ad's small print was clear about the basis for the claim.
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