Currently the world financial situation is such that expensive exploration for new oil wells becomes less and less tempting. The successful oil business today is rather driven by the necessity to extract more oil out of any existing oil well, than previously considered desirable or indeed possible.
The various techniques to achieve this are called Enhanced Oil Recovery (EOR). Common for most EOR is some form of liquid or gaseous injection into the well under high pressure. The objective being to force more oil out of the reservoirs for collection.