In the oil and gas industry, deadlegs - pipe sections without through-flow - often pose hydrate control challenges to gas and oil production systems. The hydrate challenges, if not properly managed, can cause severe consequences in terms of safety and cost for oil/gas production. This paper provides an overview of deadlegs in oil and gas production systems with some examples of typical challenges faced in the oil industry. Two different types of vertical deadleg experimental systems have been developed to acquire a better understanding of hydrate risks in gas-dominated deadlegs. These systems offer valuable quantitative information on hydrate deposit, such as thickness, porosity, morphology, growth rate, distribution, temperature profile, and amount of water and/or gas consumed as a factor of time in the deadleg system.