another test run under similar continuous injection mode conditions with vapor heated to 380 u00b0 f average temperature 19 6 w of the oil present was recovered thus it is apparent that using increased temperatures of the hydrocarbon vapor injected provides a corresponding increase in oil recovery from the tar sand the area of extracted oil was generally conical shaped with the apex near the drain hole as shown in fig3 fig4 shows a comparison of oil recovery obtained from utah tar sand with continuous solvent liquid injection and with continuous hot solvent vapor injection over about 40 hours duration it can be seen that the solvent vapor is appreciably more effective in recovering oil from the tar sand than solvent liquid apparently due to the higher temperature and greater mobility of the vapor also it was unexpectedly noted that sand plugging problems sanding in the drain holes from the vessel were substantially reduced with solvent vapor injection as compared to steam injection additional experiments were conducted using utah tar sands hot packed into the reactor vessel as per example 1 to simulate its original condition with the injection of hot solvent vapor being made about 3 34 from the top and also about 3 34 from the bottom of the vessel fig4 shows a comparison between injection of hot toluene solvent vapor near the top of the simulated tar sand formation and its injection nearer the bottom without a cored intervening passageway it can be seen that the injection of hot vapor nearer the top of the simulated formation is more effective for recovery of bitumen and is the preferred injection mode specifically in run no 13 with top injection of toluene vapor a.