* Repsol executives in Calgary for bid talks - source
* Offer could value Talisman at up to $8 billion - FT
* Talisman shares up 34 percent (Adds advisor, possible timing and background)
By Jose Elías Rodríguez and Carlos Ruano
MADRID, Dec 12 (Reuters) - Spanish oil major Repsol SA is finalising an offer for Canada's Talisman Energy Inc and has sent executives to Calgary to step up talks, a source with knowledge of the matter said on Friday.
Repsol, keen to take advantage of lower U.S. shale valuations in the face of falling oil prices, said in November it had $10 billion or more available to buy oil and gas targets in OECD countries that offer a 7 or 8 percent investment return.
"Repsol executives are in Canada but no offer has yet been made," the source said on condition of anonymity, adding the executives were from the corporate and legal departments.
The potential bid could be in a range between $6 and $8 per Talisman share, the Financial Times said, valuing the stock at a premium of up to 118 percent to its closing price on Thursday and putting a price of as much as $8 billion on the company as a whole.
Shares in the Calgary-based company, Canada's fifth-largest independent petroleum producer, rose 33.6 percent to C$5.69 at 1630 GMT, while Repsol shares fell 5.6 percent to 16.25 euros in Madrid.
Talisman said on Monday it had been approached by a number of parties, including the Spanish oil group, with regard to various transactions, but that there was no assurance that any deal would be agreed.
A Talisman spokesman on Friday declined to comment beyond the previous statement. Repsol declined to comment.
The Spanish oil firm, which hopes to clinch a deal before Christmas, has been searching for an acquisition to fill a funding gap after the seizure of its Argentine business.
It has focused its hunt on Canada to compensate for a loss-making investment in the Canaport liquefied natural gas terminal, where it is now seeking a partner.
A first round of talks with Talisman collapsed this summer, sending its shares down 63 percent since an August peak, partly because of North Sea assets that have missed production targets and weighed on its stock, sources said at the time.
Most of the projects, located in Britain and Norway, are held in a joint venture with China's Sinopec, making it difficult to quickly exit the region.
A separate source recently told Reuters the two companies had renewed talks in September but they were also inconclusive.
Due diligence was carried out during first round of talks this summer. JP Morgan is advising Repsol. (Additional reporting by Scott Haggett in Calgary; Writing by Julien Toyer and Tracy Rucinski; Editing by David Holmes)