You may notice each fall that gasoline prices begin to lower during the colder months. This is due to differences in gasoline blending, specifically increasing the amount of butane in the mix to adjust for seasonal weather changes. 

Butane’s role in gasoline blending throughout the year is a critical one with economic benefits. Butane is a natural gas liquid that serves multiple purposes, both as a fuel and a key feedstock for many important everyday products including personal protective equipment, health and hygiene products, pharmaceutical ingredients, safe packaging and more.

Butane transported through the Mariner East pipeline system is delivered to Energy Transfer’s Marcus Hook Industrial Complex (MHIC) in southeastern Pennsylvania, where it is processed and stored, or blended into gasoline for local and regional delivery. 

Ultimately, Energy Transfer blends butane into gasoline at 94 automated butane injection sites in 26 states. This typically occurs at terminals before the product is loaded onto trucks, and at times is injected directly into our pipelines. We own the only U.S. patented Automated Butane Blending System that continuously monitors gasoline flows, creates additional gasoline through butane blending, and ensures all gasoline meets specific state and federal parameters.

Butane has the highest vapor pressure of the usual components in gasoline blending. That means, during the summer, the butane level in gasoline must be low in order to meet the appropriate state and federal specifications for vapor pressure. In colder months, it must be increased to meet those same specifications.

Each blend of gasoline is tested for three parameters related to vapor pressure: Reid vapor pressure (RVP), a measure of the gasoline’s volatility, or the vapor pressure within a closed vessel; TVL, or the temperature at which the vapor-to-liquid ratio is 20%; and T50, which is the temperature at which 50% of a tested fuel is vaporized.

Because butane is a less-expensive blending component than most other ingredients in gasoline, fall and winter gasoline blends are less expensive to produce than lower-butane-level summer blends. Butane is also abundant, increasing overall gasoline supply during the cold-weather months, further reducing prices for consumers at the pump. Winter butane blending is a win-win with major benefits for Pennsylvania consumers.

As the leaves fall each year in Pennsylvania, so do gasoline prices — and we have abundant butane to thank.