Varieties of gas and oil

 

Understanding "gas" and "oil" requires looking at their chemical structures (how many carbons they have) and their physical states (gas vs. liquid). 

1. The "Gas" Family

Most fuel gases are hydrocarbons. The main difference is the length of their carbon chain and how they are stored. 

• Methane (
  

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  ): The simplest hydrocarbon (1 carbon). It is the primary component of "natural gas".
• Natural Gas: A naturally occurring mixture, mostly methane (70–90%), but it also contains ethane, propane, and butane.
  • Dry Gas: High methane content, ready for pipelines.
  • Wet Gas: Contains extra "liquids" like propane and butane that must be separated.
• Propane (
  

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  ): A 3-carbon gas. It is often sold as LPG (Liquefied Petroleum Gas), which is propane squeezed into a liquid under moderate pressure so it fits in portable tanks.
• LNG (Liquefied Natural Gas): This is methane cooled to a "cryogenic" -260°F (-162°C) until it turns into a liquid. It is not pressurized like propane; it is just very, very cold so it can be shipped across oceans in massive tankers. 

2. Varieties of Oil (Crude Oil)

Crude oil is a "soup" of many different hydrocarbons. It is classified primarily by its density and purity. 

Variety	Description	Characteristics
Light Crude	Low density; flows easily like water.	Preferred by refiners; produces more gasoline and diesel.
Heavy Crude	High density; thick and "sticky" like molasses.	Harder to pump; used for asphalt and heavy fuel oils.
Sweet Crude	Low sulfur content (usually <0.5%).	Easier to refine; named "sweet" because it doesn't smell like rotten eggs.
Sour Crude	High sulfur content.	Requires expensive processing to remove sulfur; smells like rotten eggs.

Benchmarks: You often hear of Brent Blend (from the North Sea) or WTI (West Texas Intermediate). These are specific regional "brands" of oil used as global pricing standards because they are both Light and Sweet. 

At normal room temperature and sea-level pressure, all the substances we discussed (methane, propane, butane) want to be gases. To make them easier to transport, we have to force them into a liquid state because liquids take up roughly 1/600th the space of gas. 

There are two ways to win this battle: Squeezing (Pressure) or Freezing (Temperature). 

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1. The "Squeezable" Gases (LPG / Propane)

Some gases have relatively high boiling points. They don't need much "convincing" to become liquid. 

• Propane and Butane: These are medium-sized molecules. You can turn them into a liquid just by applying moderate pressure at room temperature.
• The Tank: This is why your backyard BBQ tank or a large propane tank is heavy steel. It’s holding that pressure. Inside the tank, the propane is a liquid, but a small amount "boils" off into gas at the top, which travels to your grill.
• Term: This is called LPG (Liquefied Petroleum Gas). 

2. The "Stubborn" Gases (Methane / Natural Gas)

Methane is a tiny, energetic molecule. No matter how hard you "squeeze" it at room temperature, it refuses to become a liquid. 

• CNG (Compressed Natural Gas): Since we can't liquidize it with pressure alone, we just "scrunch" it together. It stays a gas, but it is under immense pressure (3,000+ psi). This is used for city buses and delivery trucks.
• LNG (Liquefied Natural Gas): To turn methane into a liquid, you must remove almost all its heat. You have to cool it to -260°F (-162°C). At this point, it turns into a liquid that can be poured into insulated (thermos-like) tanks for shipping across the ocean. 

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