A method for inhibiting the formation of gas hydrates in a petroleum fluid having hydrate-forming constituents is claimed. More specifically, the method can be used to treat a petroleum fluid, such as natural gas conveyed in a pipe, to inhibit the formation of a hydrate flow restriction in the pipe. The preferred hydrate inhibitors used for practicing the method comprise substantially water soluble homopolymers and copolymers of isopropylmethacrylamide derivatives which have a bimodal molecular weight distribution.