NBC, which paid just under $900m (£485m) for broadcast and online rights to the Games, said visitors to its site have viewed 456m pages and watched close to 22m video clips.
On the day of the opening ceremony on August 8, 4.2m visited the . Traffic rose to 7.8m on Monday, when the US swimming team won the 4x100m relay final. NBC recorded 1.7m downloads of its race coverage.
The first two days of TV coverage by NBC has seen 114m viewers tuning in over the first two days, with an average audience of 34.2m during the opening ceremony, 35% above the number that watched the Athens games in 2004.
In the UK, the BBC has not released information on traffic for its online Olympic coverage.
The broadcaster's coverage of the opening ceremony drew 4.9m viewers while its live afternoon coverage of the competition has been in the 2.5m-3.5m range and its 7-8pm evening highlights package in the 4m-4.5m range.