Poly(N,N-dimethylhydrazidoacrylamides)s (PDMHAMs) and a series of copolymers of (N,N-dimethylhydrazidoacrylamide) and (N-isopropylacrylamide) were recently investigated as kinetic hydrate inhibitors (KHIs). Poly(N-vinylcaprolactam) (PVCap) and related copolymers have been used as a class of commercial KHIs in the oil and gas industry to prevent plugging of pipelines with gas hydrates. In this study, we have synthesized and investigated the ability of copolymers of DMHAM monomer and VCap monomer to inhibit structure II gas hydrate formation in high-pressure rocking cells at approximately 75 bar. Various polymer molecular weights have been investigated at various pH conditions. It was found that the novel polymers have high cloud points in deionized (DI) water or brine solutions at high or low pH under pressure compared to polyVCap. A 1:2 copolymer of DMHAM/VCap gave the best KHI performance for this class of copolymer with a cloud point at 50 degrees C in DI water. Also, a 1:1 DMHAM/VCap copolymer gave excellent KHI performance, as well as giving no cloud point up to 100 degrees C in DI water or high-salinity solutions (3.615 wt % NaCl) at pH 5.0. The cloud point was found to be 67 degrees C at pH 12.0 for the 15 wt % NaCl solution, making it compatible for use in high-salinity water-based deep-water drilling fluids. It was also found that high pH improved the performance of the KHIs compared to otherwise identical tests at pH 5.0. This may be related to removing the structure I (SI)-forming and relatively more soluble acid gas CO2 from the system at high pH.