We investigate both the time-series and cross-sectional variation in the CDS-bond basis, which measures the difference between the CDS spread and cash-bond implied credit spread, for a large sample of individual firms during the financial crisis. We test several possible explanations for the violation of the arbitragerelation between cash bond and CDS contract that would, in normal conditions, drive the basis to zero.Our findings do not uncover a clear single explanatory factor for the anomaly. Rather they point towards several drivers related to funding risk, counterparty risk and collateral quality that force the individual bond basis into negative territory at different phases of the crisis.