The type of plastic that is used for oil and gas pipelines is typically high-density polyethylene (HDPE). HDPE is a type of thermoplastic polymer that is known for its high strength, toughness, and chemical resistance. It is also resistant to UV radiation and has a relatively low coefficient of thermal expansion, making it well-suited for use in outdoor environments.

HDPE is widely used for oil and gas pipelines due to its ability to withstand the high pressures and temperatures that are often encountered in these applications. It is also resistant to many chemicals that are commonly found in oil and gas, including hydrocarbons and corrosive acids.

In addition to HDPE, other types of plastic that may be used for oil and gas pipelines include polyvinyl chloride (PVC) and polypropylene (PP). These materials also have good chemical resistance and mechanical properties, but may not be as durable or resistant to high temperatures as HDPE. The specific type of plastic that is used for a particular oil and gas pipeline will depend on the specific requirements of the application.