to work out a likely target size oil/gas company's without trying to get to technical for you do a lot 2D/3D imagery and magnetic survey's that estimate the likely volume to be held in a structural trap, basically they can estimate the volume of oil that would be held in the trap, but drilling is obviously the only way to discover if the oil is still present.
looks like 16-16.5c is once again the floor for GBP today, a few buyers starting to lurk at those levels again.
GBP Price at posting:
16.5¢ Sentiment: None Disclosure: Not Held