A nuclear magnetic resonance (NMR) measurement system for high pressure and temperature measurements on fluids is disclosed. The system has a sensor assembly that includes a sample holder having a body formed from a non-magnetic metal and defining an interior cavity for receiving a fluid sample, a frame member disposed in the interior cavity of the sample holder, an antenna coil disposed in the interior cavity about the frame member, an inlet that allows the fluid sample to enter the interior cavity, an outlet that allows for the fluid sample to be flushed from the interior cavity, and a magnet assembly having a central bore in which the sample holder is disposed. Adjacent to the sample holder are pulsed field gradient coils for performing diffusion measurements. The system further includes pulse sequencer circuitry that supplies signals to the antenna coil. When the interior cavity of the sample holder is filled with the fluid sample, the antenna coil and the frame member are at least partially submerged in the fluid sample, and the antenna coil obtains NMR measurements of the fluid sample in response to the signals. Related methods and apparatuses are also disclosed herein.