* Euribor-EBF chief says testing new model for benchmark
* Euribor and Libor are key gauges for bank borrowing
* Benchmark could use mix of market rates and estimates
* Model for scandal-tainted Libor also being reviewed
By John O'Donnell
BRUSSELS, Sept 26 (Reuters) - The euro interbank offered rate could in future be calculated partly on the basis of real market prices rather than solely bank estimates, the group that oversees the lending benchmark said on Wednesday.
Euribor and larger counterpart Libor are Europe's key gauges of how much banks pay to borrow from peers and underpin swathes of financial products from Spanish mortgages to derivatives contracts in London.
The decision by Euribor-EBF to review how the euro benchmark it is calculated mirrors events in London, where regulators are expected to propose that Libor is anchored to real transactions following a rate-rigging scandal that has left more than a dozen banks under investigation.
Earlier this year, sources told Reuters that the European Central Bank was calling for a rethink on Euribor, including shifting the basis of the calculation to actual lending rates instead of the current system, which like Libor uses banks' assessments of what they expect to be charged.
Euribor-EBF said it is now examining this option.
"We are testing things in collaboration with the European Central Bank," its chief executive Guido Ravoet told journalists.
"It could well be that we go to a hybrid system where, on the one hand, when there are enough transactions, you can work on real transactions. But where there are not enough transactions, it will still be based on estimates."
Euribor, launched with the euro in 1999, takes estimates from many of the same banks as Libor.
Regulators have not yet shown evidence of manipulation in Euribor, and the benchmark's organisers - an arm of the European Banking Federation - say the number of banks involved in determining the rate would make it difficult to fix.
But the European Commission is investigating possible collusion on the Libor and Euribor rates. The EU's executive has the power to impose heavy fines if it finds wrongdoing.
The ECB may also play a closer role in supervising the benchmark, sources have said.
It is already involved in setting one of Europe's key market rates, Eonia, an overnight lending rate that ECB monetary policy is designed to steer in order to control inflation.
Unlike Euribor and Libor, Eonia is already priced from real transactions provided by a panel of banks.
Replicating this for Euribor could, however, be complicated by the current reluctance of banks to lend to one another, which would make it difficult to establish actual borrowing rates. (Reporting By John O'Donnell; Editing by John Stonestreet)