We have studied the limits of supersaturation in binary alkane mixtures and recombined crude oils at elevated pressures. Our study has interrogated these fluids using an optical cell with an internal volume of approximately 1 mu L that includes a thermally pulsed wire which nucleates bubbles to "break" supersaturation, thereby acting as a reference. In parallel, we have made measurements in a larger and more conventional optical cell with an internal volume closer to 1 mL absent the aid of a nucleation device. For both, we demonstrate a maximum supersaturation of approximately 800 psi for conventional black oils. In contrast, supersaturation is demonstrated to be minimal for volatile oils. We show that the higher surface tension of conventional black oils favors surface-mediated nucleation, while the lower surface tension of volatile oils gives rise to nucleation that primarily takes place in the bulk. Among the surfaces studied, optically smooth high-pressure windows that permit observation of the nucleation process show the lowest tendency to nucleate bubbles.