Wax crystallization is a serious problem because it may result in the plugging of wellbores, production facilities, and transportation pipelines during oil production. This study describes the use of a novel high-pressure ultrasonic detection system as a reliable technique to evaluate the wax appearance temperature (WAT) and the wax precipitated curve (WPC) of both crude oil [stock tank oil (STO)] and live oil at pressures up to 22.87 MPa. The oil sample was from Kingfisher ((F) oilfield, which is a typical high waxy reservoir. Transit time and amplitude were demonstrated to be good indicators for WAT determination with the ultrasonic method, which could not only self-verify but also distinguish the different stages of the complex process of wax crystallization. In addition, differential scanning calorimetry (DSC) and the rheometry method under ambient pressure were also presented to match the ultrasonic method. The obtained WAT data are comparable to results from DSC and rheometry, which could be used to further optimize the modeling of wax deposition. Moreover, the amount of wax precipitated could also be estimated by the ultrasonic method, and the WPC is very close to the curve obtained by DSC. It is also concluded that WAT experiments on live oils must be conducted because the measured dead oil WAT may provide too conservative and unrealistic estimates because of the composition and pressure difference. Thus, for oil production and transportation, the addition of solution gas or just to maintain the dissolution gas in contact with the crude oil may reduce the risk of wax precipitation and then drop all of the costs related to wax removal. For high-waxy oilfields, such as KF reservoirs, multiphase production and transport may be an economic solution.