The purpose of this paper is to discuss the internal surface area basis, a key issue of modeling fouling in enhanced heat transfer tubes, and to correct an error in the author's previous paper, Li and Webb [Int. J. Heat Mass Transfer 45 (2002) 1685]. A fouling factor can be defined based on one of the two area bases, nominal internal surface area and total internal surface area. The error was originated from incorrect definition of internal surface area basis. (C) 2003 Elsevier Ltd. All rights reserved.