Non-bank lenders have ramped up their lending for buyouts since the summer, doubling the number of mid-market deals in the third quarter amid success by private debt funds in raising new money this year.

Private debt funds - or non-bank lenders, which raise money from investors for deals - completed a total of 24 mid-market deals in the third quarter of the year, compared with 11 deals in the second quarter and seven in the first quarter, according to research by Deloitte released on Tuesday.