This paper describes a volumetric strategy for characterization of tumor blood flow using microbubble (MB) contrast agents and ultrasound (US) imaging. Volumetric contrast-enhanced US (VCEUS) imaging was implemented on a SONIX RP US system (Ultrasonix Medical Corp) equipped with a broadband 4DL14-5/38 probe. Acquisition of VCEUS data was achieved at a volume rate of 1 Hz using a MB sensitive harmonic imaging mode. Following MB infusion, custom Matlab programs were used to compute MB time-intensity curve-specific parameters: blood volume (I PK), transit time (T 1/2PK), flow rate (S PK), and tumor perfusion (AUC). Using a xenograft model of human breast cancer, it is shown that millimeter-sized deviations in transducer positioning can have profound implications on US-based blood flow estimators with errors ranging from 6.4 to 40.3% and dependent on both degree of misalignment and particular blood flow estimator. These errors indicate that VCEUS imaging should be considered in tumor analyses because they incorporate the entire mass and not just a representative planar cross-section.