During the performance of a contract, unanticipated circumstances can arise which increase a contractor’s costs. Sometimes, the contract allocates the risk of the unexpected event as, for example, when a contract provides that the agency will bear the risk if a contractor encounters a differing site condition that increases the contractor’s costs. In other circumstances, a principle of common law establishes which party will bear the risk of an unexpected occurrence. For example, case law provides that an agency’s failure to disclose facts to a contractor can, in some circumstances, result in the agency’s bearing the risk of unanticipated performance difficulties that increase the contractor’s costs.