Portal 2 was originally going to feature five main gels: Repulsion, Propulsion, Adhesion, Conversion, and a fifth as-yet-unnamed type. After activating Pump Station Delta and Adhesion Gel, an extra underground testing track would have contained Pump Station Epsilon and 'Gel Epsilon.' "Aperture originally created this Gel E as a healthy sandwich spread, which would also provide energy...[snip]
EDIT:
Apparently there's a post length limit, full interview here: http://tinyurl.com/2g9mqh

