The collateralized debt obligation in particular enabled financial institutions to obtain investor funds to finance subprime and other lending, extending or increasing the housing bubble and generating large fees. This essentially places cash payments from multiple mortgages or other debt obligations into a single pool from which specific securities draw in a specific sequence of priority. Those securities first in line received investment-grade ratings from rating agencies. Securities with lower priority had lower credit ratings but theoretically a higher rate of return on the amount invested.