Su!"mary. The ~ariati~n ~twee~ thickening-time test results from tests on pilot blends and cement-blend sample tests has been a subject of frequent InvestigatIOn. DIsagreement between these test results is often blamed on improper additive proportioning inadequate blending, or incorrect sampling techniques.' A comprehensive study of blending, sampling, and testing variables was conducted. This paper describes the results ,)f this research testing with a full-scale laboratory bulk plant. It also includes the results of a south Texas field study in which thickening time test results from more than 300 cement-blend samples were examined. Results of these studies suggest that significant statistical variations may be in~o~ved i.n ble~din¥, sampling, and ~esting pr~u.r~~ under deep-well conditions. The variabilities are used as guidelines for determInIng thlckerung-ttme acceptance WIndows. Vanabillttes or uncertainties can be minimized by optimization and standardization of these procedures. Re.ult. of Full·Scale Laboratory Blending and Sampling StudyCement-blend uniformity tested after even-numbered pneumatic transfers indicated that a minimum of four moves was required for adequate blending. 20 Cement-Blend Composition Class H cement, 3% (BWOW*) KCI, 0.2% low-temperature retarder Class H cement, 35% silica flour, 20% hematite, 3% KCI, 0.75% dispersant, 0.5 0 AJ fluid-loss additive Class H cement, 35 0 AJ silica flour, 70 0 AJ hematite, 13 0 AJ (BWOW) NaCI, 1.0% dispersant, 0.7 0 AJ fluid-loss additive, 0.25 0 AJ defoamer Class H cement, 3 0 AJ KCI, 0.15 0 AJ low-temperature retarder Class H cement, 35 0 AJ coarse silica, 27 0 AJ hematite, 0.5 0 AJ dispersant, 0.40AJ fluid-loss additive Class H cement, 35 0 AJ silica flour, 320AJ. hematite, 37 0 AJ NaCI, 0.9% low-temperature retarder, 0.25 0 AJ defoamer Class H cement, 35 0 AJ silica flour, 32 0 AJ hematite, 13 0 AJ NaCI, 0.2% dispersant, 0.8 0 AJ fluid-loss additive, 0.25% defoamer Class H cement, 35 0 AJ coarse silica, 46 0 AJ hematite, 0.75 0 AJ dispersant, 1.3% high-temperature retarder Class H cement, 35 0 AJ silica flour, 56 0 AJ hematite, 13% NaCI, 1.0 0 AJ dispersant, 0.7 0 AJ fluid-loss additive, 0.25 0 AJ defoamer Class H cement, 35 0 AJ silica flour, 3 0 AJ KCI, 0.25 0 AJ dispersant, 1.0 0 AJ fluid-loss additive Class H cement, 35% silica flour, 32 0 AJ hematite, 13% NaCI, 0.20AJ dispersant, 1.0 0 AJ fluid-loss additive, 0.20AJ high-temperature retarder, 0.25 0 AJ defoamer Class H cement, 35 0 AJ silica flour, 70% hematite, 13 0 AJ NaCI, 1.0 0 AJ dispersant, 0.7 0 AJ fluid-loss additive, 0.25 0 AJ defoamer Class H cement, 35% silica flour, 70 0 AJ hematite, 13% NaCI, 1.5 0 AJ dispersant, 0.7% fluid-loss additive, 0.25 0 AJ. defoamer Class H cement, 35% coarse silica, 8 0 AJ hematite, 13 0 AJ NaCI, 0.20AJ dispersant, 0.7 0 AJ fluid-loss additive, 0.20AJ high-temperature retarder, 0.25 0 AJ defoamer Class H cement, 35 0 AJ silica flour, 84 0 AJ hematite, 13% NaCI, 1.0% dispersant, 0.7 0 AJ fluid-loss additIve, 0.25% defoamer Class H cement, 85 0 AJ silica fl...