The Collaborative International Dictionary of English v.0.48:

Porterage \Por"ter*age\, n.
   1. The work of a porter; the occupation of a carrier or of a
      doorkeeper.
      [1913 Webster]

   2. Money charged or paid for the carriage of burdens or
      parcels by a porter.
      [1913 Webster]

WordNet (r) 3.0 (2006):

porterage
    n 1: the charge for carrying burdens by porters
    2: the transportation of burdens by porters