The private-equity firms Advent International Corp. and Bain Capital LLC are seeking $2.1 billion of loans to fund their bid to buy Royal Bank of Scotland Group PLC's credit card payment processing unit, two people familiar with the matter said Monday.

Lenders led by RBS, Goldman Sachs Group Inc. and UBS AG are arranging the deal, which includes about $620 million of mezzanine debt, said the people, who declined to be identified because the information is private.

Spokesmen for Advent and Bain declined to comment.

The deal would add to $5.3 billion of buyout financing underwritten in Europe this year, 53% more than during the same period last year, according to data compiled by Bloomberg. RBS, taken over by the U.K. government in 2008 after credit losses forced it to seek a bailout, is the most active underwriter of all types of leveraged loans in Europe.

Advent and Bain, both based in Boston, have entered exclusive talks with RBS to buy its RBS WorldPay unit, people with knowledge of the matter said on July 23, and an agreement may be announced by Aug. 6.

WorldPay operates in more than 40 countries and provides credit card payment processing services to clients including small and midsize businesses. It's among the 10 largest processors of online payments in the U.S.

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