BP's shares rallied as investors speculated on rumours of a takeover bid by US energy giant Exxon Mobil.The oil and gas company has been surround by market chatter of a takeover since its share price was hit by the Gulf of Mexico disaster in 2010.BP has been forced to pay compensation after the explosion and sinking of the Deepwater Horizon oil rig which caused the biggest oil spill in US history. One analyst however suggested to Sharecast however that the Exxon rumours should be taken "with a pinch of salt," perhaps as a result of the light news flow on Friday. RD