A hydrate is a physical combination of water (H₂O) and other small molecules producing a solid, which has an ice-like appearance but possesses a different molecular structure. Formation in gas and/or natural gas liquid (NGL) systems can plug pipelines, equipment and instruments, and restrict or interrupt flows. There are three crystalline structures for hydrates. In each, H₂O molecules – host molecules – build the lattice, and hydrocarbons, nitrogen (N₂), xenon (Xe), argon (Ar), carbon dioxide (CO₂) and hydrogen sulfide (H₂S) – guest molecules – occupy the cavities. Smaller molecules such as methane (CH₄), ethane (C₂H₆), CO₂ and H₂S stabilize the body-centered cubic called Structure I. Larger molecules propane (C₃H₈), isobutane (iso-C₄H₁₀) and n-butane (n-C₄H₁₀) form a diamond-lattice called Structure II. Molecules larger than n-C₄H₁₀ do not form hydrates as they are too large to stabilize the lattice.¹