A total of 2.9 million tickets have been sold - but 2.5 million are still available, some at major events.
The men's and women's 100 metre finals, now likely to be run in front of thousands of empty seats.
The men's and women's tennis finals, which was supposed to be one of the highlights of the Games.
The men's 1,000 metres, javelin, shot put and 5,000 metres competition, which were to form part of the festival of athletics.
The closing ceremony, which is still to sell out despite the opening receiving critical acclaim.
Embarrassed organisers had hoped to outclass the 2000 Games in Sydney, acknowledged as the best ever, by branding the event as the Olympics "coming home".
Instead, most of Athens has left to escape the summer heat and only a fraction of the visitors who were supposed to come have turned up. Many have been put off by the lastminute rush to compete the Olympics venues fearing they would be sitting in half-finished stadiums.
Fears of a terrorist attack have also blighted ticket sales. Greeks now seem to be buying fewer tickets after their 200 metre sprinter Kostas Kenteris was caught up in a doping scandal.
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