A stackable flask for the culturing of cells is disclosed. The cell culture chamber is defined by a top plate and a rigid bottom tray of substantially rectangular shape connected by side and end walls, the body of the flask has imparted therein a gas permeable membrane that will allow the free flow of gases between the cell culture chamber and the external environment. The flask body also includes a sealed septum that will allow access to the cell growth chamber by means of a needle or cannula. The size of the flask and location of an optional neck and cap section allows for flask manipulation by standard automated assay equipment, making the flask ideal for high throughput applications.