The mud/gas log, sample log, electrical logs and the logs resulting from computer analysis of full suites of electrical logs, are all powerful tools for the evaluation of exploratory wells. However, none is infallible. There have been instances when one picks up the indications of a productive zone and the others do not. Any one (or two or even all three) may fail to recognize a productive zone. This paper discusses how this may happen, and cites some examples.