This paper presents the results of imbibition tests using a reservoir crude oil and a reservoir brine solution with a high salinity and a suitable nanofluid that displaces crude oil from Berea sandstone (water-wet) and single-glass capillaries. The Illinois Institute of Technology (IIT) nanofluid is specially formulated to survive in a high-salinity environment and is found to result in an efficiency of 50% for Berea sandstone, compared to 17% using the brine alone at a reservoir temperature of 55 degrees C. We also present a direct visual evidence of the underlying mechanism based on the structural disjoining pressure for the crude oil displacement using IIT nanofluid from the solid substrate in high-salinity brine. These results aid our understanding of the role of the nanofluid in displacing crude oil from the rock, especially in a high-salinity environment containing Ca2+ and Mg2+ ions. Results are also reported using Berea sandstone and a nanofluid containing silica nanoparticles.