Can flex fuel cut your petrol bill? What the Brazil model shows us

As India gears up to launch E85 fuel on World Environment Day (May 5), a key question for motorists is simple: Will a flex-fuel car actually save money at the pump? 

The answer is more complicated than a straightforward yes or no. Brazil, the world’s most successful flex-fuel market, offers some important lessons for India as the country prepares for higher ethanol blends such as E85 and E100. 

But, what is a flex-fuel vehicle? 

A flex-fuel vehicle (FFV) can run on varying mixtures of petrol and ethanol. Depending on the model, this can range from E20 (20% ethanol) to E85 (85% ethanol) or even E100 (pure ethanol). The engine automatically adjusts to the fuel blend, allowing drivers to choose whichever fuel is available and economical. 

MUST READ | Petrol, EV or Flex-Fuel? Here’s which car makes most sense for your road trips in 2026

India has already completed the nationwide rollout of E20 fuel and is now considering regulations for E85 and E100 fuels. Carmakers including Maruti Suzuki, Toyota, Honda and Hero MotoCorp have begun showcasing flex-fuel-ready vehicles. 

The Brazil story: Why it matters 

Brazil is often cited as the gold standard for flex-fuel adoption. 

The country built an extensive ethanol ecosystem over decades, using sugarcane as the primary feedstock. Today, flex-fuel vehicles dominate Brazil’s market, and the country has been able to replace a significant portion of its petrol consumption with domestically produced ethanol. Industry estimates cited in policy discussions indicate Brazil replaced roughly half of its petrol demand with ethanol through widespread blending and flex-fuel adoption. 

The secret to Brazil’s success wasn’t just vehicle technology — it was economics. 

The 70% rule 

Brazilian motorists follow a simple thumb rule. 

Because ethanol contains less energy than petrol, vehicles generally travel fewer kilometres per litre when running on high ethanol blends. As a result, ethanol only makes financial sense when its price is sufficiently lower than petrol. 

In Brazil, drivers often use the “70% rule”: if ethanol costs less than about 70% of petrol’s price, it is usually the cheaper fuel on a cost-per-kilometre basis. If ethanol is priced higher than that threshold, petrol becomes the better deal. 

DON’T MISS | Here’s how many petrol pumps will offer E85 flex-fuel by 2026-end

This is the biggest lesson for India. 

What do flex fuel costs look like in Brazil?

Brazil’s experience shows that the real comparison is not the sticker price at the fuel pump, but the cost of every kilometre travelled.

Recent examples from Brazil illustrate why. In early 2026, average petrol prices in many parts of the country were around R$6.30 per litre, while ethanol was selling for about R$4.10 per litre. That puts ethanol at roughly 65% of petrol’s price, making it the cheaper option despite lower fuel efficiency.

However, when ethanol prices rise to around R$4.70 per litre while petrol remains at R$6.30 per litre, the ratio jumps to nearly 75%. At that point, many Brazilian motorists switch back to petrol because the mileage loss outweighs the lower fuel price.

The reason is that ethanol typically delivers 25-30% lower mileage than petrol because it contains less energy per litre. Brazilian drivers therefore use the famous “70% rule”—ethanol generally makes financial sense only when it costs no more than about 70% of petrol’s price.

What would this mean for India?

For Indian consumers, the lesson is straightforward. If petrol costs ₹100 per litre, ethanol would likely need to be priced at around ₹70 per litre or less for most flex-fuel vehicles to offer meaningful savings on a cost-per-kilometre basis.

DO CHECKOUT | BT Explainer: What are flex-fuel cars and how they differ from EVs & hybrids?

Anything significantly above the 70% threshold could reduce or eliminate the financial advantage of using ethanol, even if the price per litre appears lower. That is the key lesson from Brazil’s decades-long flex-fuel experiment: the cheapest fuel is not always the one with the lowest pump price — it is the one that delivers the lowest cost per kilometre travelled.

Will Indian drivers save money? 

Not automatically. 

While ethanol is generally cheaper to produce domestically than imported petrol, vehicles running on E85 or E100 typically deliver lower mileage because ethanol has lower energy density. That means drivers may need more fuel to travel the same distance. 

Industry executives have already warned policymakers that consumers will adopt flex-fuel vehicles only if E85 and E100 are priced significantly below petrol. Otherwise, any savings from cheaper fuel could be cancelled out by lower fuel efficiency. 

In other words, the fuel bill depends not on the price per litre, but on the cost per kilometre travelled. 

India’s infrastructure challenge 

Another lesson from Brazil is that fuel availability matters as much as vehicle availability. 

Brazil built a nationwide network where motorists can easily choose between petrol and ethanol at fuel stations. India is still in the early stages of building that ecosystem. 

The government plans to establish around 5,000 ethanol dispensing stations by the end of 2027, but industry experts say a “chicken-and-egg” problem remains. Automakers want wider fuel availability before launching large numbers of flex-fuel vehicles, while fuel retailers want more flex-fuel vehicles on the road before investing heavily in infrastructure.