Optoacoustic imaging, a novel noninvasive modality, combines the advantages of optical methods and the ultrasound technique. The optoacoustic technique is based on tissue irradiation with nanosecond laser pulses and detection of ultrasound waves generated due to thermo-elastic expansion. Using a modified Monte Carlo technique and solution of wave equation for velocity potential, we modeled optoacoustic signals from cylindrical blood vessels with varying oxygenation and varying total hemoglobin concentration. A specially designed computer code was used for reconstruction of images of absorbed energy in the blood vessels and surrounding tissues. Then we performed a set of experiments with our optoacoustic system and phantoms that simulate blood vessels such as veins and arteries at depths of up to 2 cm. The optoacoustic signals from the phantoms were used for reconstruction of 2-D cross-section images and correlated well with geometry and optical properties of the phantoms. The obtained data suggest that the developed optoacoustic imaging approach can be used for accurate mapping of blood oxygenation and hemoglobin concentration in blood vessels.