Kinetic hydrate inhibitors (KHIs) are water-soluble polymers designed to delay gas hydrate formation in gas and oilfield operations. Inhibition of growth of gas hydrate crystals is one of the mechanisms by which KHIs have been proposed to act. One class of commercial KHIs is the hyperbranched poly(ester amide)s. We have investigated the ability of a range of structurally different hyperbranched poly(ester amide)s to inhibit the crystal growth of tetrahydrofuran (THF) hydrate which forms a Structure 11 clathrate hydrate, the most common gas hydrate structure encountered in the upstream oil and gas industry. The results indicate that there is an optimum size of hydrophobic groups attached to the succinyl part of the polymer, which gives best crystal growth inhibition. However, total inhibition was impossible to achieve even at a concentration of 8000 ppm of one of the best polymers at a subcooling of 3.4 degrees C, tentatively suggesting that polymer adsorption onto natural gas hydrate crystal surfaces is probably not the primary mechanism of kinetic inhibition operating in field applications with this class of KHI. (C) 2009 Elsevier Ltd. All rights reserved.