Shares in oil giant Royal Dutch Shell rose more than 4% before closing at their highest level in six months on Thursday as traders cited rumours of a possible tie-up with a rival.
"There's a mutter of a BP/Royal Dutch tie-up," said one trader.
Other traders also noted the BP rumour while one analyst reported talk of a tie-up with Russia's Gazprom, which the analyst said may have stemmed from a research report from Shell's house broker ABN Amro.
Shell and BP representatives declined to comment. ABN could not immediately confirm the report.
Shares in BP closed 2.4% up at 570-1/2 pence while other oil stocks also gained thanks to a rise in oil prices. The DJ Stoxx European oil and gas sector index was up 2%.
One analyst said Shell shares were also likely supported by comments from a spokesman that the Anglo-Dutch oil giant had started work to restore 170,000 barrels per day (bpd) of crude oil production in Nigeria, after a protest at a major pipeline hub hit output.
While industry sources said BP's former CEO had considered a tie-up with Shell a few years ago, BP sources said new CEO Tony Hayward planned to focus on fixing BP's operational issues rather than big strategic actions in the coming months.