The Petroleum industry is divided into three major operations: Upstream,
Midstream and Downstream.
There are many definitions for these operations but I believe the ones below are generally accepted.
The Upstream operation, also known as the Exploration and Production (E&P) sector, covers the activities from the drilling an oil and gas well to separation processes of gas and crude oil until the export operation. Midstream operations typically involve transporting the oil from the platform to the refining complex. The Downstream operation is a term commonly used to refer to the refining of crude oil, the selling and distribution of end products (including natural gas).