The oil and gas industry is usually divided into three major sectors: upstream, midstream, and downstream.
The downstream sector is the refining of petroleum crude oil and the processing and purifying of raw natural gas,[1] as well as the marketing and distribution of products derived from crude oil and natural gas.
The oil refining process commonly includes hydrodesulfurization which converts most of that sulfur into gaseous hydrogen sulfide.
The hydrogen sulfide removed in the refining and processing of crude oil and natural gas is subsequently converted into byproduct elemental sulfur.
[3][4] Marketing is the wholesale and retail distribution of refined petroleum products to business, industry, government, and public consumers.