Midstream assets refer to the infrastructure and facilities within the energy industry that are crucial for transporting, storing, and processing oil, natural gas, and byproducts. After upstream operations have extracted raw energy commodities, midstream services bridge the gap between extraction (upstream) and the point where they are refined and made ready for consumer use (downstream).

Midstream assets typically include:

1. Pipelines: Extensive networks that transport oil and natural gas across vast distances.
2. Storage Facilities: Large tanks or underground spaces where oil or gas can be kept until demand rises or until it is transported further.
3. Processing Plants: Facilities where raw natural gas is purified and separated into its constituent parts, such as methane, propane, and butane.
4. Fractionation Units: Installations that separate the components of natural gas liquids into individual hydrocarbons.
5. LNG Terminals: These are used for liquefying natural gas for storage or transport and regasifying LNG back into a gaseous state.
6. Railcars and tanker trucks: Specialized vehicles for transporting oil and gas where pipelines are not available.
7. Gathering Systems: A network of small-diameter pipes that collect oil or gas from various wells and transport it to processing plants or larger pipelines.

Investing in midstream assets can offer a stable income stream, primarily through fee-based contracts, as the volume of commodities transported, stored, or processed is less subject to fluctuations in commodity prices compared to upstream activities.

For more information about Midstream assets, the following resources could be helpful:

1. The American Petroleum Institute (API) website provides extensive resources on the oil and natural gas industry, including the functions and importance of midstream assets: (https://www.api.org/oil-and-natural-gas/wells-to-consumer/transporting-oil-natural-gas)

2. The U.S. Energy Information Administration (EIA) website is a highly reputable source for energy statistics and analysis. They offer a plethora of information about all segments of the energy sector, including midstream operations: (https://www.eia.gov/energyexplained/natural-gas/transportation-of-natural-gas.php)

Please note that while these URLs are active and valid as of my last training data, web content can change, so you should confirm that the web pages are still available and offering the expected information about midstream assets.