Why is it “9/10 of a gallon”? It isn’t—it’s nine‑tenths of a cent per gallon

It’s not 9/10 of a gallon; the “9/10” you see on U.S. fuel price signs is nine‑tenths of a cent added to the per‑gallon price. The convention dates to the 1930s, when taxes and price competition pushed stations to advertise fractional‑cent prices, and it persists today largely because of marketing psychology and industry habit. Below, we explain what the fraction means, how it started, and why it remains standard.

What the “9/10” actually means

On a price like $3.59 9/10, the “9/10” is $0.009—nine‑tenths of one cent—added to the $3.59, making the true posted price $3.599 per gallon. It does not mean you receive only 9/10 of a gallon, and it’s not 9/10 of a dollar. Pumps calculate your total using the full $3.599 rate, then your receipt is rounded to the nearest cent on the final transaction amount.

How the odd fraction took hold

The practice emerged during the Great Depression and the years that followed. As governments introduced and adjusted gasoline taxes—sometimes in fractions of a cent—stations entered intense price wars where a tenth of a cent could sway motorists. Mechanical pumps and regulatory rules allowed fractional‑cent postings, and retailers discovered that ending prices with .9 (the biggest sub‑cent discount before the next whole cent) drew attention and made prices seem lower. By the late 1930s, “nine‑tenths” had become the norm and it never left, even as prices rose and electronic signs replaced hand‑set boards.

What it means at the pump, in dollars and cents

Here’s how that extra 9/10 of a cent per gallon affects real purchases, from the math to how your receipt is calculated.

• Per‑gallon math: $3.59 9/10 equals $3.599. That extra 0.009 dollar is less than one cent per gallon.
• Typical fill‑up impact: For 15 gallons, 0.009 × 15 = $0.135. You’ll pay about 14 cents more than if the price were $3.590.
• Rounding on receipts: Pumps compute the exact total (e.g., 15.000 × $3.599 = $53.985) and the payment system rounds the final charge to the nearest cent ($53.99 in this example).
• Displayed vs. settled price: The fractional‑cent is always included in the posted price; it’s not a separate fee and isn’t added after the fact.

In short, the 9/10 increment is small on a per‑gallon basis but noticeable over a full tank, and it’s always embedded in the price you see and the total you pay.

Why stations still use 9/10

Several forces keep nine‑tenths pricing alive, even in the era of digital signs and algorithmic pricing.

• Marketing psychology: A price that looks a cent lower (e.g., $3.59 9/10 vs. $3.60) can nudge drivers, similar to $19.99 retail pricing.
• Competitive signaling: When every nearby station posts in 1/10‑cent increments, dropping or raising by exactly 0.1¢ helps match rivals precisely.
• Industry inertia: Decades of custom, pump software defaults, and signage formats assume fractional‑cent endings.
• Regulatory compatibility: Weights‑and‑measures rules allow fractional‑cent display and calculation, so there’s no legal pressure to abandon it.

Taken together, these incentives make the practice sticky: even if consumers roll their eyes, stations fear standing out by rounding to whole cents when competitors do not.

Is it unique to the United States?

No. Fractional‑cent fuel pricing appears in other countries, too—often per liter rather than per gallon. Canada commonly posts 162.9¢/L (that .9 is a tenth of a cent), and the U.K. and parts of Europe often show tenths of a penny or euro‑cent per liter. While the exact tax history and market dynamics differ, the psychological appeal of “just‑under” pricing is widespread.

Could the 9/10 disappear?

It could, but it’s unlikely soon. Some retailers occasionally experiment with whole‑cent pricing for simplicity, and modern digital signage makes any format feasible. Still, as long as competitors stick with fractional‑cent endings—and consumers continue to respond to just‑under pricing—most stations have little incentive to change. Any broad shift would probably require a coordinated industry move or a regulation mandating whole‑cent postings, neither of which appears imminent.

Summary

The “9/10” on gas price signs isn’t 9/10 of a gallon—it’s nine‑tenths of a cent added to the per‑gallon price, a Depression‑era artifact of taxes and competition that endures thanks to marketing psychology and industry convention. It slightly increases a fill‑up total—by about a dime or so on a typical tank—and, despite occasional calls to round to whole cents, remains standard practice in the U.S. and common in other countries.

When did gas hit $1.00 a gallon?

The national average price for a gallon of gas first hit $1.00 in the fall of 1979, primarily due to the Iranian Revolution and the ensuing energy crisis, which disrupted oil production and significantly increased oil prices. 
Here’s a more detailed timeline of events:

• Late 1970s: The average price of gasoline was rising significantly, with prices nearing $1.00 per gallon in some places. 
• Fall 1979: The national average price of a gallon of gasoline officially crossed the $1.00 mark. 
• Context: This surge in prices was a direct result of the Iranian oil embargo and revolution, which led to a sharp increase in crude oil prices and a decrease in oil supply. 
• Aftermath: While prices initially exceeded $1.00, they fluctuated, with the national average dipping below $1.00 again in the mid-1980s before consistently staying above that threshold in the later 1980s and beyond. 

Why is gas sold by 9/10 of a gallon?

A one-cent price swing when gas is selling for 10 cents per gallon meant a 10% change. Over time, fuel retailers evolved to pricing at 0.9 cents. The reason is marketing. Retail experts have long known that goods prices slightly less than those priced at a whole number sound far less expensive.

When was gasoline $0.10 a gallon?

Fractional prices first appeared in the early 1900s as states and the federal government implemented gas taxes to help build and maintain highways. Back in the 1930s, when gas was just 10 cents a gallon, adding a penny would seem like a huge increase by 10%, so they went with less than a cent.

What does the 9/10 mean for gas prices?

For gas, the “9/10” signifies nine-tenths of a cent added to the price, a practice dating back to the Great Depression when it was used to pass on a small federal and state tax without a full penny increase. While the fraction is now a meaningless marketing tactic to make prices seem lower, the total you pay is rounded up or down to the nearest cent because you can’t physically pay in fractions of a cent. 
Why it started

• To absorb a tax: In the 1930s, a federal gas tax was implemented to fund roads. 
• To avoid significant price jumps: With gas costing only a few cents a gallon, a full penny increase would have felt like a massive 10% markup for consumers. 
• To soften the blow: Gas stations passed the tax on by adding a fractional amount, like 9/10 of a cent, which was a smaller, less noticeable increase. 

Why it continues 

• Psychological pricing: Gas stations discovered that ending prices in a “9/10” (like $3.499) makes the price appear substantially cheaper than a rounded-off price (like $3.50).
• Historical inertia: The practice simply stuck around as prices evolved and became more expensive over time.

How it affects you

• You still pay in whole cents: Opens in new tabThe 9/10 of a cent is a marketing strategy for the display price, but your final charge will be rounded up or down. 
• It adds up for consumers: Opens in new tabWhen millions of gallons of gas are sold daily, even a fraction of a cent per gallon can add up to hundreds of millions of dollars for gas stations and fuel companies annually.