The ECB funding would be used to fill the gap between loans and deposits in Spain and Portugal, with EUR6.2bn being earmarked for Spain, where lenders are exposed to the real estate market crash.
Barclays CEO Bob Diamond said the offer of cheap cash had been "very positive" in restoring market confidence.
The loan could be a more efficient way to fund local operations than providing sterling-denominated funds from headquarters, according to Reuters.
The bank said any funding benefit would not be used to contribute to the remuneration of any personnel.
RBS has bagged EUR5bn in the second offer, the first offer in December 2011 was also a similar amount, as reported by Reuters.
ECB has been offering more than EUR1 trillion of loan, to safeguard the banks against collapsing due to currency crunch.
