In December 2003 Standard and Poor's introduced "Recovery Ratings" designed to indicate the likely "loss given default" rather than the "likelihood of default" indicated by their traditional ratings. They range from one+ (high expectation of 100% recovery of principal) to five (negligible expectation of recovery of principal 0 - 25%). A survey of 2,800 debt instruments over 10 years, undertaken in 2004, demonstrated that despite initial concerns, the risk profile of the project finance asset class was comparable to that of senior secured corporate debt and the average recovery rate was 75% on defaulted loans (with a default rate of 12%). UK PFI project loans typically have recovery ratings higher than this average, because of the termination compensation arrangements and, in a few cases, explicit debt underpinning. For example, Transport for London substantially underpinned the debt taken on by Metronet and Tubelines to finance the London Underground PPP. The first securitisation of 24 UK PFI projects by DePfa Bank Plc had an estimated post default recovery rating averaging 85% for debt funders.