A reservoir containing approximately 12 billion bbl of original oil in place (OOIP) has produced only 1 billion bbl after 15 years of primary production, with the reservoir pressure declining from 11,500 to 4,100 psi, rapidly approaching the bubblepoint pressure of 3,750 psi. Miscible displacement with high-pressure nitrogen injection has been selected as an enhanced-oil-recovery (EOR) process for the naturally fractured thick carbonate reservoir containing light oil underlain by an aquifer. The objectives are to maintain the reservoir pressure and increase the ultimate recovery.