A method for inhibiting formation of hydrocarbon hydrates in mixtures of water and a hydrate-forming guest molecule has been discovered that involves adding a composition to the mixtures in an amount that is effective in inhibiting formation of the hydrocarbon hydrates under conditions otherwise effective to form the hydrocarbon hydrates in the absence of the reaction product. The composition includes at least one dendrimeric compound having a number average molecular weight of at least 1,000 atomic mass units (amu); and at least one small molecular weight species having less than 1,000 amu, selected from the group consisting of polyalkyleneimine, polyallylamine, starch, sugars, and polymers or copolymers of vinyl alcohol or allyl alcohol; and, optionally, at least one surfactant.