One of the problems associated with running ad-hoc queries in an OLTP system is lock contention. Compensation-based query processing has been proposed as a solution to this problem. In this paper, undo/no-redo compensation is used to bring inconsistent copies of the base relations into a transaction-consistent state. Queries process the database internal log to obtain information on updates made by concurrent transactions. A performance analysis of the algorithm shows that it can be executed efficiently in an OLTP system with low to medium system utilization.