INTRODUCTION Pressure loss data are presented for single-phase Newtonian* fluid flow normal to banks of plain tube rows. The data cover a wide range of regular arrays of in-line and staggered tubes and allowances are given for known temperature variations through the bank. However@ for the particular types of tube arrangements shown in Table 3.1@ Item No. 79034 (Reference 4) may be preferred because it is easier and more consistent to use due to the more detailed treatment given to such tube geometries. Item No. 79034@ however@ does not consider the effects of by-passing for which this Item may be used. It should be noted that the notation and method of this Item are different from those of Item No. 79034 but the relationships that link the two notations are given in Appendix D. Complementary to this Item on pressure loss is Item No. 73031 (Reference 3) which can be used to calculate the heat transfer data; the two Items are compatible in terminology and notation. The flow around a bank of tubes is a complex phenomenon?? and there are therefore many factors which influence the pressure loss. Some of these factors can be allowed for systematically by the methods described in Sections 4 and 5. Other factors which are known to be significant but unquantifiable are discussed in Section 8. The comprehensive calculation process takes into account the following effects: (i) fluid property variations due to temperature variations@ (ii) by-passing@ (iii) tube inclination@ (iv) tube outside surface roughness@ (v) upstream turbulence intensity@ (vi) number of tube rows in direction of crossflow. For some applications@ the refinements given by considering all the above effects may not be necessary. Section 3.3 therefore offers guidance on simplifying the full calculation procedure and enables checks to be made on any consequent losses of accuracy. Section 9 gives details on the uncertainty and limitations of the data. * Most pure liquids and simple mixtures of pure gases are Newtonian; non-Newtonian fluids include paints@ polymer solutions@ etc. ?? Appendix C offers simple physical explanations of the flow around the tubes and may help the user to recognise and to deal with situations where the determination of pressure loss is difficult.