This communication presents an extensive comparison of three transient methods (Perers, DSC and Wijeysundera) for testing solar flat-plate collectors. Results from different tests are compared with the steady state values obtained on the basis of the ASHRAE 93-86 standard. Based on the experimental results, it is seen that Perers＇ method yields parameters closer to the steady state values. The sensitivity analysis shows that the results of Perers and DSC methods are greatly affected by measurement errors; whereas the Wijeysundera method is less sensitive. Comparison of the prediction of outlet temperature with measurements for the Perers and DSC methods show that the values based on the later method are closer to the measurements. (C) 2000 Elsevier Science Ltd. All rights reserved.