(Reuters) - Penn Virginia Corp's (>> Penn Virginia Corporation) shares rose as much as 15.5 percent on Thursday following a report that BP Plc (>> BP plc) had offered to buy the U.S. oil and gas producer for $8 per share.

The offer, which values the company at about $573 million (364 million pounds), represents an 80 percent premium to Penn Virginia's Wednesday close of $4.45. The company's shares were trading at $5 on Thursday afternoon.

Penn Virginia has rejected the offer saying it undervalues the company, financial news website Proactive Investors reported, citing sources familiar with the situation.

BP declined to comment, while Penn Virginia was not immediately available for comment.

(Reporting by Anannya Pramanick in Bengaluru; Editing by Saumyadeb Chakrabarty)