The inhibition characteristics of kinetic hydrate inhibitors were experimentally investigated by utilization of the ultrasonic testing technique. PVCap (poly(vinylcaprolactam)) and VP/BA (vinyl pyrrolidone/butyl acrylate) were chosen as two typical kinetic inhibitors. Results of the tests demonstrate two kinds of inhibition mechanisms of kinetic hydrate inhibitors, i.e., nucleation inhibition and growth inhibition. PVCap polymer is strong to retard catastrophic growth of hydrate formation, while VP/BA dominantly prevents hydrate nucleation. The synergism of glycol ether compounds on the performance of PVCap was also tested. It was found that glycol ether compounds noticeably prolong the nucleation time, and extend the delay of catastrophic growth significantly. (C) 2010 Elsevier Ltd. All rights reserved.