We investigate several complexity issues related to branch-and-cut algorith
ms for 0-1 integer programming based on lifted-cover inequalities (LCIs). W
e show that given a fractional point, determining a violated LCI over all m
inimal covers is NP-hard. The main result is that there exists a class of 0
-1 knapsack instances for which any branch-and-out algorithm based on LCls
has to evaluate an exponential number of nodes to prove optimality.