This value indicated that ultrasound power has high impact during in-situ transesterification of soybean oil with increasing methanol to oil ratio. Similar results were also reported by Qian et al. (2008). The effect of ultrasound power on various methanol to oil ratio on oil to biodiesel conversion rate is shown in Fig. 9. The figure shows that increasing ultrasound power increased the oil yield. The coefficient of determination factor had a value of R2=0.89 with high ultrasound power, whereas low power obtained R²=0.25. These results confirmed the lower ability of methanol on oil extraction without ultrasonication effect in comparison with other solvents or alcoholic mixtures. Similar results were reported on methanol effect during biodiesel production by (Kim et al., 2010; Qian et al., 2008).