INTRODUCTION This Data Item presents information on static-pressure recovery@ total-pressure loss and overall flow pattern for fluids flowing through straight-axis@ plane-walled diffusers of rectangular section having only one* or two? walls diverging. Data are presented for diffusers operating under certain basic conditions noted in Section 3. For other conditions the data available are insufficient to allow more than a general indication of trends to be given in Sections 4 to 6. Examples of the application of the Item are given in Section 7. * As in Sketch 5.1. ? As in Sketch 1.1.