The natural gas delivery chain comprises three groups: upstream (generally associated with the production aspect of the industry), midstream (generally associated with the transmission aspect of the industry), and downstream (generally associated with the distribution aspect of the industry. The midstream sector consists of entities involved in moving gas from production areas to the citygate and in storing gas until it is ready to be used. Different entities use the term midstream to refer to different sets of assets. Some include gathering systems and gas processing in the definition of midstream, while others consider this to be part of the upstream production sector. 

The graphic below shows parts of the gas delivery system that are considered to be midstream. The dotted line shows components that are sometimes considered part of midstream, while solid line shows components that are always considered part of midstream:



Following is a description of each market participant in the midstream sector. First are participants in the physical delivery system:

Gathering system
Gathering systems are pipelines that connect to lease facilities and carry the production gas to a processing facility. Gathering systems often connect multiple wells owned by multiple producers. Some consider gathering systems to be part of the upstream production sector, others consider them to be part of the midstream sector. 

Gas processor
Gas processing facilities take raw gas from gathering systems and process the gas to produce pipeline quality natural gas as well as other valuable natural gas liquids (NGLs). The processing facilities also remove contaminants. Some consider gas processors to be part of the upstream production sector, others consider them to be part of the midstream sector. 

Interstate pipeline
Pipelines transport gas from producing regions (or supply basins) to market regions. 

Storage provider
Storage providers operate storage fields and offer storage services to a variety of market participants. Pipelines, LDCs, and hub operators also provide short-term storage known as balancing and/or parking. 

Hub operator
Hub operators provide various services at points where multiple pipelines intersect. These include wheeling between pipelines, exchanges, title transfers, price discovery, electronic trading, and parking and lending. 

The following market participants don’t own facilities, but perform market functions in the midstream sector:

Marketers generally purchase gas supplies from producers or aggregators and then resell the gas to end users, LDCs or other marketers.

A broker is an entity that matches buyers and sellers of gas without ever taking title to the gas itself. This differentiates a broker from a marketer in that marketers actually buy and sell gas while brokers simply match up buyers and sellers. Brokers also often provide advisory services such as supply/demand, price, and weather forecasting, as well as assistance with transportation, storage, and clearing arrangements.

A shipper is any market participant holding a contract to transport gas on a pipeline or LDC. Shippers may be end users, marketers, producers, or other LDCs.

Financial services company
Financial services companies assist market participants with products that help them hedge the risk of price fluctuations. Many market participants do not wish to or cannot tolerate the risk of price fluctuations that occur in a commodity market. For these participants, the fee charged by financial service companies is a small price to pay for insulation from market variables. 

Electronic trading exchange
Centralized electronic trading exchanges provide a place for market participants to trade commodity and standardized financial products.