AOL was recently relaunched as a free portal, and both AOL and MSN have seen a decline in dial-up subscribers.
Julian Smith, European online advertising analyst at Jupiter Research, said: "It appears that both are struggling against the likes of Yahoo and Google, so this is perhaps a logical defensive action which could boost advertiser numbers by combining the subscriber base."
The move comes soon after MSN launched an advertising option similar to Google's AdWords in a bid to catch up with the model created by the search giant.
Other analysts speculate that links between the two could increase the probability of a closer merging of their instant messaging platforms.
"Communications such as instant messaging and VoIP are becoming increasingly important, so that will be a target as well," said Smith.
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