An on-demand drinking adapter for use with a beverage container is disclosed. The adapter includes a base with an upper surface and generally cylindrical sides which extend below the upper surface. The cylindrical sides are adapted for temporarily fastening the adapter to a mouth of a beverage container. The adapter also includes a spout with a vertically extending surface, a second surface, and an on-demand drinking aperture. The spout extends above the upper surface and the vertically extending surface is curved and coextensive with a portion of the cylindrical sides.