Downstream operations, in the oil and gas industries, include refining and distribution, as opposed to upstream (exploration and production).
The major oil companies tend to be integrated (have both upstream and downstream operations) whereas the smaller ones tend to specialise.
Downstream operations tend to be highly competitive, although often oligopolies. Downstream margins are much less dependent on oil prices than upstream margins, as the input and output prices tend to move together: although the oligopolistic nature of the industry can make sales prices a little sticky in the short term.
The oligopolistic nature of the market, together with the more stable margins, makes downstream operations a much more predictable source of profits than upstream. However, the dominance of downstream by the big integrated oil companies, means that there is little pure play exposure to this business available.