There are a number of oil and gas recovery methods which can utilize nitrogen. They range from the simplest (pressure maintenance) process to the most complex (miscible) technique. The common factor in all of these processes is the use of nitrogen. Perhaps one of the oldest, and yet simplest methods of oil recovery (gas injection), is a growing application for nitrogen. Pressure maintenance can include immiscible displacement as well as enhanced gravity drainage. Due to nitrogen being inert and non-explosive, it is quickly replacing the usage of natural gas in the applications.