Abstract: In testing the condition of well bore formations as to fluid flow into and out of the surrounding formations and gas emission therefrom prior to cementing a production casing in the well bore, a testing fluid of a preselected density, such as a salt water solution, is pumped from a source through a treating conduit into the production casing positioned in the well bore. The testing fluid is circulated down the production casing and up the annulus between the production casing and well bore formations displacing drilling fluid and other materials therefrom. For an empty well bore the production casing and annulus are filled with the testing fluid. Samples of the fluids are directed periodically to a gas detector to test for the presence of gas emitted from the formations surrounding the well bore. Once the well bore is flushed clean, the testing fluid is conveyed through a closed circulating system of conduits to a storage vessel.