The displacement of one fluid by another (miscible or immiscible) in porous media is an important phenomenon that occurs in groundwater movement arid oil reservoir engineering. Practical examples are water flooding, solvent flooding, saltwater intrusion into coastal aquifers, and coning. Experiments are presented on viscous fingering in Hele‐Shaw models. The use of Hele‐Shaw cells facilitates fundamental studies of the viscous effects. For an immiscible displacement the dispersive and the relative permeability phenomena are absent. This investigation covers the entire scope of finger development from the incipient fingers predicted by Chuoke's theory to a parallel‐sided single finger. Results of several experiments run in a Hele‐Shaw cell with and without local heterogeneities show the wavelength degeneration to one finger for different flow conditions and the initial number of fingers. It was also found that the rate of growth develops almost immediately, well before the fingers are parallel sided. The mechanisms of wavelength generation and degeneration are di
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