An inverse solver for the estimation of the temporal-spatial heat transfer coefficients (HTC), without using prior information of the thermal boundary conditions, was used for immersion quenching into palm oil, canola oil, and two commercial petroleum oil quenchants. The particle swarm optimization (PSO) method was used on near-surface temperature-time cooling curve data obtained with the so-called Tensi multithermocouple, and a 12.5 by 45 mm Inconel 600 probe. The fitness function to be minimized by a PSO approach is defined by the deviation of the measured and calculated cooling curves. The PSO algorithm was parallelized and implemented on a graphics accelerator architecture. This article describes, in detail, the PSO methodology used to compare and differentiate the potential quenching properties attainable with vegetable oils versus those attainable with accelerated and conventional petroleum oil quenchant.