I don't have the original one on hand. The research I encountered was done at the University of Victoria back in the 1980s, and I learned about it while I was a student there.

However I just looked at http://en.wikipedia.org/wiki/Paper_cup#Environmental_impact which has the comment, Paper cups may consume more non-renewable resources than cups made of polystyrene foam (whose only significant effluent is pentane). which includes two citations for the fact.