Shares in Dana Petroleum were down in afternoon trading on the FTSE 250 after it said it would not be supporting a £1.7 billion takeover bid from the state owned Korea National Corp (KNOC).
KNOC also said that it would be raising its bid and refused to sign a confidentiality agreement to examine Dana's books.
Dana claimed that KNOC had not acknowledged offers from the company for its executives to travel to South Korea for talks, following the failure of earlier talks in Canada.
Dana, which mainly explores for oil in the North Sea and in Africa, said that its earlier invitation for talks still stood, but added that it planned to "pursue actively all opportunities to maximise shareholder value".
By 16:20 shares in Dana were down 4.25 per cent on the FTSE 250 to 1621.00 pence per share.