One of the markets at the heart of the credit bubble has surged back with surprising speed as investors chasing yield are increasingly willing to finance riskier companies.

Poster children of the mid-2000s credit bubble, leveraged loans are set to have their busiest year since 2008, thanks to a rush of money into the market from investors looking for high-yielding alternatives to stocks and junk bonds. It is a boon for speculative-grade companies looking to refinance and for private-equity firms hoping to start a buyout wave.

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