This marks the second time that the account has switched agencies in as many years - in November 2000 Exxon Mobil handed its media account to Zenith Media after making the decision to cut back its agency roster.
Zenith beat Carat, Starcom, Universal McCann, OMD and MediaVest in a competitive pitch in this review, which was led out of Exxon Mobil's headquarters in Virginia.
However, sources suggest the client has now realigned its media account into Omnicom's OMD network.
Exxon Mobil is the world's biggest oil company and owns the Esso, Exxon and Mobil brands. It was created after the $81 billion merger of Exxon and Mobil in November 1999, with Exxon forming the larger part of the business.
Like most of its competitors Exxon Mobil has cut its advertising spend - according to AC Nielsen MMS it spent less than £1 million supporting its brands in the UK last year.
Esso has become a target for anti-capitalist campaigners. Recently there has been speculation that Exxon Mobil would drop the Esso brand in the UK in favour of Exxon and drop its Pricewatch plan, but this has been flatly denied.
No-one at either Exxon Mobil or OMD was available for comment on the story as Campaign went to press.