Aberdeen-based exploration firm Dana Petroleum has had a £1.87bn ($2.9bn) hostile takeover offer from South Korea's state-owned oil company Knoc.
The offer is the equivalent of £18 per share, 59% above Dana's share price of £11.51 before Knoc's interest was first announced.
This latest bid follows the Dana board's rejection of Knoc's approaches earlier this month.
South Korea hopes a successful takeover would boost its oil reserves.
"We are very disappointed that the board of Dana does not agree that 1,800 pence per share represents a full and fair value for the company," Knoc senior executive vice-president Kim Seong-hoo said in a statement.
He appealed to shareholders to agree to the offer, saying it represented "full and fair value" for the company.
The company says it has already gained the support of 48.6% of shareholders. This is considered a particularly high proportion at this stage in a takeover attempt and close to the 50% level at which the bid will be considered to have been successful.
Some analysts therefore think the deal will go ahead without Knoc raising its offer.
Knoc also sought to reassure employees that it was not planning any operational changes.
Dana issued a statement saying it "notes" the cash offer. It urged shareholders not to act until it issues an update on its production and exploration activities at the end of the month.
Last week, it said that Knoc's offer did not take account of developments that had so far not been made public, but were set to increase Dana's oil production and reserves.
Dana's board refused to open its books to Knoc and broke off discussions with it after the South Korean firm refused to sign a confidentiality agreement.
Established in the late 1970s, state-owned oil company Knoc is engaged in some domestic oil exploration and production, but in recent years has tried to build up the country's oil reserves through a series of international acquisitions.
If successful, the Dana takeover would be Knoc's biggest to date.
Dana, which last year made profits of £54m, mainly operates off the coast of the UK, but also has production facilities off West Africa and in Egypt.