The phase behavior and minimum miscibility pressure (MMP) for nitrogen with light oils were studied. The phase behavior studies were performed on N/sub 2/ hydrocarbon mixtures as well as N/sub 2/ recombined oil systems at high pressures (above 4,000 psia). The synthetic oil system of N/sub 2/ C/sub 1/ C/sub 4/ C/sub 10/ was studied to approximate the phase behavior of crude oils with nitrogen and to investigate the effect of the presence of methane on phase behavior and N/sub 2/ MMP values. The phase behavior data are used in a computer simulator to match the slim tube displacement behavior and to provide an estimate of the MMP. The N/sub 2/ recombined oil studies provide the complex behavior of multicomponent systems. Adjustment of parameters to predict the phase envelope has been made in order to use these parameters in equations-of-state (EOS) for predictions at various reservoir conditions. This provides a cross-check of the conditions of miscibility achieved during the slim tube experiments. Experimental runs were performed in a slim tube apparatus to determine the MMP of stock-tank oils with nitrogen, recombined oils, and synthetic oils at pressures up to 10,000 psia and temperatures from 200 to 300 F. These experiments were performed using stock-tank oils with API gravities of 50.8/sup 0/ and 61.5/sup 0/, recombined at different gas-oil ratios (GOR). The experimental results indicate the important contribution of light and intermediate components of crude oil in decreasing the MMP and show the variation in oil recovery as a function of temperature. Similar N/sub 2/ MMP tests were performed on two synthetic mixtures containing C/sub 1/, C/sub 2/, C/sub 3/, C/sub 4/, C/sub 5/, C/sub 6/, C/sub 7/, C/sub 8/, C/sub 9/, C/sub 10/, and C/sub 12/. These studies will provide useful information for the implementation of the N/sub 2/ miscible displacement process. 26 refs., 28 figs., 7 tabs.