Using spectral photoacoustic imaging (sPAI) to estimate oxygen saturation of tissue at depth suffers from inaccuracies due to the unknown optical absorption and scattering properties of tissue. Because of the high scattering and absorption of light by tissue, the estimation of concentrations of Hb and HbO2 from the measured photoacoustic (PA) signal intensity can be erroneous. Simulation of wavelength-dependent light transport in tissue can help to estimate the local fluence distribution within the tissue. In this work, a Monte Carlo simulation has been implemented to simulate the fluence distribution in placental tissue. We obtained sPAI images of ex vivo human placental tissue and demonstrate improved estimations of hemoglobin oxygen saturation by using a fluence correction derived from the Monte Carlo simulation. The results show that with simulation correction, the oxygen saturation value is 12.61±3% which is closer to the value 6.8% directly measured from ex vivo human placenta using invasive oxygen probe.