Drove 20 km at 5 a.m. and every gas station was empty: how a fuel price map app climbed past Waze in France

A small French studio that had a Room Temperature Thermometer with 7M installs. In 2026, European fuel prices kept rising and stations kept running out, so it used free government fuel price data to build an app for finding cheap gas. Six months after launch, it reached #2 in the France Google Play Maps & Navigation free chart, behind only Waze and ahead of several veteran apps that had been around for over a decade. This piece covers what it is, why now, where the users come from, where the money comes from, and whether you can follow it.

Sep 30, Colmar

On Sep 30, 2026, a French user left a one-star review on the app's store page: "I just installed it, and it told me a station in Colmar had fuel. I drove 20 km at 5 a.m. and it was all empty. Nothing but wasted fuel."

The developer replied the same day, in English.

That review captures this app's situation. People really are desperate for fuel, so they install it. But the information it shows, like every app of its kind, can only be "the last time we knew." Ten days earlier, on Sep 20, 15% of France's stations were short of at least one fuel type (per TF1info and that day's Le Parisien report). Two days later, the government extended the summer diesel sales period to Nov 15.

What it is

The French store name is "Carburant : essence moins cher" (cheaper fuel), the UK name is "Petrol Prices & Fuel Finder," the US name is "Gas Prices & Fuel Finder," and the brand name is FuelSaver. The features are what you'd expect: a map and list of nearby prices, cheapest marked green and most expensive red, sorting by price or distance, filtering by brand, showing when each price was last updated, calculating the cost to fill your tank based on its size, and one-tap navigation. The store description says "30 countries," and the website fuelsaver.one says 45.

The data costs nothing. France uses official prices from data.economie.gouv.fr, Germany uses Tankerkoenig, Austria uses E-Control, and the UK uses the GOV.UK Fuel Finder, which became mandatory to publish from Feb 2026 2. The developer also registered the app as a "reuse" case on data.gouv.fr.

Behind it is Codelio, an independent French mobile studio whose Play developer account is named APPVERSE. Its big hit is Room Temperature Thermometer, with 6.98M installs, ranked #2 in the France weather chart. It also makes flashlight, notepad, VPN, and recorder tools. In other words, this is a company that already runs "free tools + ads + ad-free subscription" well, and the fuel app is a new product on the same model with different data.

How fast it grew

Compare it with the established rivals on the France maps chart the same day (Google Play, 11-06):

Its cumulative total is only one-tenth to one-twentieth of theirs, but its new installs this week are 2.5 to 4.5 times theirs. Almost all the growth is on Android: iOS added only 58 ratings in a week.

Why now: two fuel crises in one year

2026 brought two waves of fuel crisis in Europe. The first was in 3, April. The Strait of Hormuz was blockaded, French fuel prices rose, and some stations ran out. By Apr 6, Paris-Normandie was already writing about "five apps you need during a fuel shortage." FuelSaver's iOS version launched on Apr 21 and the Play version in May, right at this moment.

The second wave came in September: prices spiked again and shortages spread widely. Le Monde published a shortage map on Sep 24, and in October the average diesel price was about 2.35 €/L (supercarbu.fr).

The reviews show this cause and effect directly. From mid-September, review volume surged, and the five-star reviews almost all say the same thing:

"Actuellement, c'est tellement important de connaître les prix des carburants." (Knowing fuel prices is so important right now.) — Jean-Pierre Vinot, 9-13

"En cette période de précarité, votre application est plus que nécessaire." (In this time of hardship, your app is more than necessary.) — Walter Baert, 9-14

"Avec les temps qui courent, le moindre centime est important !!" (In times like these, every cent counts!!) — muriel deruelle, 10-12

The demand came from the news, not from the product.

Where users come from: the store, not social media

Searching TikTok for "carburant moins cher" or "fuelsaver" turns up no videos promoting it. On French TikTok, the recommended content is Essence&CO, Gasoil Now, and TotalEnergies promotions. On X, nobody has mentioned it in nearly 60 days, and French media recommendation lists are all veteran apps. Its installs come almost entirely from Google Play itself, driven by three things:

A local keyword title in each country. "Carburant : essence moins cher," "Prix Essence & Carburant," "Petrol Prices." The names match the terms people type in the store, instead of the brand name FuelSaver.

Very high ratings. 4.9 stars, versus about 4.0 for the rival Gasoil Now and about 3.5 for Essence&CO. Many five-star reviews are one or two words, like "Super" or "top" or "c'est Super merci 👍." The update notes say "rating requests are shown at most once per launch," meaning there is a rating prompt on startup. The developer replies to nearly every review, often the same day. Positive reviews get "Merci ! C'est exactement ce qu'on vise 🙌," negative ones get "already fixed, please update," and one reply reads "One of our Agent fixed…" (one of our agents fixed it). The replies themselves look automated (inference).

Likely buying ads. A two-star review from Oct 24 said: "Digne d'un résultat sponsorisé sur le Play Store" (Deserves a sponsored result on the Play Store). The app is full of ads, and after a few taps a pop-up offers a premium version that "pays for itself with the first tank." An app that's six months old is adding new users at three to four times the weekly rate of a decade-old veteran, and it broke into the overall app chart at #38, which looks like Google app ads at work. But we found no ad records, so this is unverified.

It also picked up a cheap advantage: the veteran apps' ads keep getting heavier. One review reads "après ce qu'est devenue gasoil now ça change" (after what Gasoil Now has become, this is a relief). New users see a 4.9-star app with a fresh interface in search results, and they tap it.

Where the money comes from

Ads plus a subscription to remove them. The Play page lists "contains ads + in-app purchases $1.99–9.99." In August, a user complained that you couldn't skip the ads without paying. The developer replied that "now it's only 99 cents for a whole year, and the price goes up this week." The price is still being tested. The paywall's pitch is "pays for itself with the first tank."

It has never appeared on any country's Top Grossing chart, so its revenue is most likely mainly ads, and its scale is not visible from the outside (estimate).

Its ads and paywall are drawing the same complaints as the veterans: "insupportable.... pubs omniprésentes et appli payante... je garde slmc" (unbearable, ads everywhere and a paid app too... I'm sticking with SLMC), Oct 25. Earlier, in August, someone wrote "worse than Gasoil Now, I didn't think it could get worse," and 15 people found that helpful. In monetization it is no different from the veterans. It is just newer.

Who it's competing with

The last point matters most: during the same crisis, at least seven or eight similar apps appeared. Same data, same features, and only this one broke through. The difference isn't the product. It's that this one is backed by a studio that knows how to run a store, monetize, and reuse templates.

If it were you

Verdict (C): there's something to learn, but following it closely isn't worth the effort. France already has three established apps with millions of installs each, a free official website, Waze, and Google Maps, plus a wave of small copycats. This app's win came from timing and store tactics, not the product itself. As fuel prices come down, demand will fall with them.

Who it's for: small studios that already ship utility apps, have an ad SDK, a subscription paywall, a rating prompt, and multi-language templates ready to go. For you, the thing worth copying is the chain: news event → find the government's open data → ship a tool app in a few weeks → launch a local-keyword listing in every country that has data.

Who it's not for: indie devs starting from zero. Without ready-made monetization templates and store experience, you become Je Carbure Malin: a few thousand installs, working off the same data, and still not breaking out.

How to do it: don't build another French fuel-price app. Take the same method to other things where official data exists and people suddenly need to check: electricity prices, water and power outages, drug shortages, severe weather, driving restrictions. Or change the country: first look at which countries just opened fuel-price data (like the UK did in 2026 February), and start where local incumbents are weak and the title keywords aren't taken yet. On the product side, the gap to fill is the one neither it nor the incumbents handle well: "does this station have fuel right now?" The top complaints are inaccurate shortage info and missing stations.

How to get users: mainly store search. Use the local terms people actually search, not the brand name; ask for ratings at launch and reply to every review, aiming for 4.8+ stars; add a Google App Campaigns push during the ramp-up. Social platforms barely matter in this category.

When to get in: follow the event. The weeks of the crisis are the window: launch as soon as the data source opens and the news breaks. Enter after the crisis passes and only the incumbents' turf is left.

What would show we got it wrong: ① after oil prices fall back, it still holds a top 5 spot on the French maps chart, which would mean this isn't just crisis money, that retention and store placement are valuable on their own, and that following it is worth more than we estimated; ② it charts in a country's Top Grossing, which would mean ad-free subscriptions really do bring in money, not just ads; ③ another app from the same wave of copycats breaks into the top 10 without a studio behind it, which would mean the barrier is lower than we thought.

Data and sources: Google Play installs, charts and reviews (10-29 to 11-06, review text from the French store); App Store French and UK store data (10-28 to 11-06); Play French store page (11-06); fuelsaver.one, codelio.fr, data.gouv.fr; fuel crisis coverage: Paris-Normandie 04-06, TF1info, Le Parisien 09-20, actu.fr 09-22, Le Monde 09-24, supercarbu.fr October; UK Fuel Finder: fuelsindustryuk.org, petrolprices.co.uk; Gasoil Now ad growth: cartecarburant.com; TikTok and X search (11-06). Anything marked "inferred", "estimated" or "unverified" is an inference.