Shares in BG Group closed 6% higher after reports that a takeover bid may be in the offing.
The reports suggest the bid would value the gas exploration and production company at almost £54bn.
As a result of the reports, BG shares had risen 61 pence to £10.89 at the close of the market in London.
Royal Dutch Shell, Exxon Mobil and Petrobas have all been reported as possible buyers of BG in the past, but no firm bids were made.
BG was formed as part of the demerger of British Gas in 1997.
'Blood in the water'
The bid reports come at a time of increased merger and acquisition (M&A) and asset sale activity in the oil and gas sector.
On Friday, Aberdeen-based exploration firm Dana Petroleum received a £1.9bn hostile takeover offer bid from South Korea's state-owned oil company Knoc.
Earlier this week, Cairn Energy announced plans to sell up to 51% of its Indian operations to mining group Vedanta for up to £5.4bn.
"Given the background of the deals that have happened, there is blood in the water," David Hart, oil and gas analyst at Westhouse Securities, told the BBC.
One of the reasons for the "heightened sentiment in (M&A) activity", Mr Hart said, was the more stable oil price, which gave buyers greater confidence in the assets they were bidding for.
BG had a number of "very attractive assets", including offshore fields in Brazil and projects in Australia, that could well appeal to the "supermajors" like Shell and Exxon, Mr Hart added.
The reported figure of £54bn would make a deal for BG one of the biggest takeovers in the oil and gas sector.