The oil and gas industry is usually divided into three major components: upstream, midstream and downstream.
The midstream sector involves the transportation (by pipeline, rail, barge, oil tanker or truck), storage, and wholesale marketing of crude or refined petroleum products.
Pipelines and other transport systems can be used to move crude oil from production sites to refineries and deliver the various refined products to downstream distributors.
The midstream operations are often taken to include some elements of the upstream and downstream sectors.
ISO 20815 defines "midstream" in its definition section as: 3.1.27 midstream business category involving the processing and transportation sectors of petroleum industry.