Crop coefficient of cotton is estimated using two remote sensing techniques: an energy balance approach (SEBAL) and a reflectance-based method (Kcbrf). The results are compared with tabulated values in the FAO-56 paper, as well as the Kc values developed by the US Bureau of Reclamation (USBR) to be used in the "Lower Colorado River Accounting System (LCRAS)." Crop coefficients from all four sources (SEBAL, K cbrf, FAO-56, and LCRAS) are analysed to approximate daily and seasonal water requirement of cotton for the growing season of 2008. The results show that both FAO-56 and LCRAS underestimate cotton irrigation demand due to assuming a shorter growing season and ignoring a heavy pre-irrigation event. Remotely sensed estimates of water requirement were also validated using actual irrigation depth data.