Improved methods are provided for the application of downhole oil or gas well treating agents, such as liquid corrosion inhibition agents. The methods involve first lowering a liquid retainer device into a well casing, preferably at or above the location of the well production zone, followed by introduction of a liquid treating agent. The presence of the liquid retainer device prevents substantial passage of the agent into the production zone, and forms a column of the liquid agent above the device. The retainer device is then withdrawn from the well so as to create a substantially uniform film of the agent along the inner surfaces of the well casing. In this manner, proper coating of the casing is achieved while preventing production losses owing to passage of the treating agent into the production zone. The liquid retainer is preferably one or more swab cups or oil field retainers.