• 4 minutes Pompeo: Aramco Attacks Are An "Act Of War" By Iran
  • 7 minutes Who Really Benefits From The "Iran Attacked Saudi Arabia" Narrative?
  • 11 minutes Trump Will Win In 2020
  • 15 minutes Experts review Saudi damage photos. Say Said is need to do a lot of explaining.
  • 1 min Ethanol is the SAVIOR of the Oil Industry, Convenience Store Industry, Automotive Supply Chain Industry and Much More!
  • 4 hours Let's shut down dissent like The Conversation in Australia
  • 12 hours One of the fire satellite pictures showed what look like the fire hit outside the main oil complex. Like it hit storage or pipeline facility. Not big deal.
  • 10 hours Saudi State-of-Art Defense System looking the wrong way. MBS must fire Defense Minister. Oh, MBS is Defense Minister. Forget about it.
  • 19 hours Donald Trump Proposes Harnessing Liberal Tears To Provide Clean Energy
  • 11 hours Trump Accidentally Discusses Technology Used In The Border Wall
  • 18 hours Saudis Buying Oil From Iraq
  • 8 hours Ethanol, the Perfect Home Remedy for A Saudi Oil Fever
  • 9 hours Hong Kong protesters appeal to Trump for support.
  • 1 day Drone attacks cause fire at two Saudi Aramco facilities, blaze now under control
  • 3 hours Collateral Damage: Saudi Disruption Leaves Canada's Biggest Refinery Vulnerable
  • 19 hours Saudis Confirm a Cruise Missile from Iranian Origin
  • 3 hours Iran in the world market
Alt Text

Canada’s Natural Gas Crisis Is Going Under The Radar

Canadian natural gas producers continue…

Alt Text

Are Asian LNG Prices About To Rally?

LNG spot prices rose last…

Alt Text

The Natural Gas Crash Isn’t Over

After having reached their highest…

Robert Rapier

Robert Rapier

More Info

Premium Content

Lower Gas Prices Are Right Around The Corner

Fall arrives next month. Along with it comes relief from the heat, and usually at the gasoline pump as well. 

It isn’t simply that demand for gasoline drops after summer driving season. Gasoline is also cheaper to produce after summer, for reasons I explain below.

There are many different recipes that can be used to make gasoline, but the final product has to meet certain specifications. One of those is related to how quickly the gasoline evaporates, and that is influenced by the composition and the ambient temperature.

Regulating Smog

Gasoline vapors contribute to smog, so the Environmental Protection Agency (EPA) regulates gasoline blends by putting seasonal limits on the Reid vapor pressure (RVP). The RVP specification is a measure of the tendency to evaporate; the higher the vapor pressure the faster the evaporation rate.

Normal atmospheric pressure is around 14.7 lbs per square inch (psi) at sea level. As liquids are heated, the vapor pressure of the liquid rises until it reaches atmospheric pressure — at which point it boils.

Thus, vapor pressure is a function of both the substance and its temperature. Under normal atmospheric temperatures water is a liquid because its vapor pressure is well below 14.7 psi. It still evaporates (i.e., it still has a vapor pressure), but slowly.

The same phenomenon applies to gasoline. As the temperature increases, the vapor pressure rises. Thus, if gasoline blends remained exactly the same from winter to summer, the evaporation rates in summer would be much higher. That would greatly increase smog.

Related: Brazil’s Opposing Energy Views

So, EPA lowers the RVP requirement for gasoline in summer. The specific limit varies from state to state (and tends to be more restrictive in congested areas and warmer locations), but 7.8 psi is a common RVP limit in much of the U.S. in the summer months. 

Fall Means Cheaper Gasoline

In September, the RVP specifications begin to be phased back up. This lowers the cost of gasoline production by allowing the blending of more butane, which is cheap relative to most other gasoline blending components. 

Butane has an RVP of 52 psi, which means pure butane is a gas at ambient pressure and temperature. But it can be blended into gasoline, and its fractional contribution to the blend roughly determines its fractional contribution to the overall vapor pressure. As long as the total blend does not exceed normal atmospheric pressure (again, ~14.7 psi) butane can exist as a liquid in a gasoline blend.

Butane can’t make a large contribution to summer blends without driving the vapor pressure above the limit. But when the limit increases in the fall, it becomes feasible to blend larger volumes of butane. 

Related: Venezuela Takes Unprecedented Action To Stabilize Currency

Butane is cheap and abundant. Butane is a component of natural gas liquids (NGLs), the production of which have boomed along with natural gas production. Butane routinely trades at a discount of more than $1/gallon to gasoline, so gasoline blenders are happy to blend as much in as they possibly can.

So fall not only brings lower demand, but it opens up the gasoline supply to a cheap and abundant blending component. That’s why prices tend to fall as the weather begins to cool. And as summer approaches, the RVP specs tighten back up. The amount of butane that can be blended drops, just as summer driving season starts to pick back up. That’s why gasoline prices conversely rise by Memorial Day.

Up Next – The Ethanol Effect

The requirement to blend ethanol into the gasoline pool is a wildcard that has impacted gasoline blending over the past decade. I will discuss the impact of ethanol, and how a move to 15% ethanol blends can impact gasoline specifications, in the next article.

By Robert Rapier

More Top Reads From Oilprice.com:

Download The Free Oilprice App Today

Back to homepage

Leave a comment
  • Tom on August 25 2018 said:
    It will be interesting to see what the Ethanol Hater, Robert Rapier has to say about Ethanol Next time. I don't expect any of Ethanol's many benefits to be explained. Robert loves his BTEX Cancer Causing Hydrocarbons for Octane, instead of clean burning, 113 Octane, Low Carbon Ethanol.
  • Thomas on August 25 2018 said:
    Robert you forgot to mention that E-15 will also be available again starting September 16, for all vehicles 2001 and newer, cutting gasoline prices even more!

    That’s nice to know for all of us who buy gasoline to get around.

    You also forgot to mention that we could have had lower gasoline prices all summer long, if E-15 hand been available. But for that to happen Big Oil and the API would have to stop opposing it.

    E-15 is basically a higher octane replacement for E-10 Regular Unleaded Fuel. E-15 also and has a slightly lower RVP Pressure than E-10. So allowing E-15 fuel to be sold year-round would actually reduce evaporative emissions during the summer months and all year long for that matter. E-15 also burns cleaner than E-10 and has a lower carbon foot print.

    But alas, the terror of it all, E-15 crowds Big Oil’s monopoly at the gas pumps! Replacing harmful Benzene - BTEX Hydrocarbon Compounds, with something far Cleaner and Safer, High Octane ethanol!

    You see, a Cleaner Burning, Higher Octane Fuel, for a Lower Price with ethanol, sends shivers down Big Oil’s Spine. So EPA and Big Oil have to fight it, just like they fight the electric car industry!

    Oil really doesn’t care about the consumer, and that’s why they will eventually lose to ethanol and the electric auto industry.

    In the end, the consumer will win, no matter how hard Big Oil and EPA try to fight it.
  • Cowpoke on August 26 2018 said:
    I learned something new today. Thanks

Leave a comment

Oilprice - The No. 1 Source for Oil & Energy News
Download on the App Store Get it on Google Play