In the present work, noncondensable contaminant accumulation in tubes of single-pass, multiple-row, cross-flow condensers is investigated. A mathematical model of condensation in such heat exchangers is proposed, which considers changes along the tubes in the saturation temperature, coolant velocity, and heat transfer effectiveness. The model equations are solved with an original algorithm. The vapor distribution, the global effectiveness of the condenser, and the pressure drop between the inlet and outlet plena are determined under different working conditions.