Plentyoffish.com, a free online dating site which generates revenue from sending members to other dating sites, has recently released data that promiscuity among women has doubled since 2004.

The site tracked 315,478 users going to casual only dating sites in 2004. Of those users, the number of women who were looking for sex through the intimate encounter option was about 9%. Among users tracked in 2008, the number of women who were looking for an intimate encounter rose to 18%.

The statistics are surprising given that the male:female ratio of Plentyoffish.com members looking for long term relationships or traditional dates has remained consistent at 55:45.

Three years ago, men who were looking for intimate encounters online outnumbered women 10 to 1. Now, the ratio is only 5 to 1. Within a decade, it's predicted that men and women will be equally promiscuous, with a 1 to 1 ratio of those looking for intimate encounters.

Markus Frind, CEO of Plentyoffish.com explained, "Our average user, among males and females, is between 38 and 42 years old. Yet, the data shows that the behavior exhibited is more of what you would expect from those in their early 20s. Plentyoffish.com statistics may be indicative of a fundamental shift in society and behavioral norms."