The present work aims to identify and quantify underlying physics behind the formation of three-dimensional stall cell using oil flow visualization and stereoscopic particle image velocimetry (SPIV) on a two-dimensional NACA 0015 airfoil. The three dimensional structures were explored at various angles of attack (α = 14° to 18°) and Reynolds numbers (Rec = 1.62∙105 to 4.2∙105). Surface oil flow visualization was used to qualitatively identify the stall cells and resolve associated equivalent near surface skin friction. In addition, SPIV measurements were taken in order to visualize the stall cells above the surface of the airfoil. Results showed that the stall cells are highly sensitive to Reynolds number and angle of attack, with evidence of an apparent bi-stable state existing at a Reynolds number of 3.83∙105. Using SPIV the flow fields and the associated vorticity fields for the various cases were measured and correlated to the surface oil flow visualization.