Long post warning, TL;DR at the bottom.
While it first started because of a tax on gas, it's not the tax per se that lead to the protest, but the fact that this tax was put in place to compensate the elimination of a tax on "fortune".
The whole protest is now kind of a clusterfuck of demands, but most of them are around 2 themes : - Fiscal injustice - Our model of democracy
Fiscal injustice: Pretty much every french feels like the high level of taxes we pay does not end up where we want nor where it is useful. It is not really that we want less taxes, but that we want them used intelligently. Our education system gets worse and worse every year because of budget cuts. Our healthcare system gets worse and worse every year because of budget cuts. Our justice system gets worse and worse every year because of budget cuts. Our retirement and social protection in global get worse and worse because of budget cuts.
Meanwhile, we get more taxes but nobody can really see where it goes.
On top of that, our government privatize what was once the best services that could show to the world. We had world class train infrastructure at a low price. That didn't go well because of budget cuts that lead to reduction of maintenance, that lead to the classic late trains that we are now famous for. Our small train lines are getting abandoned, leading to whole part of the territory being cut out of the rest of France (in a railway point of view). Our petrol foraging was state based and profitable, so was our electricity infrastructure management and production, engineering and such. Everything is getting sold for quick cash, when it was either profitable or at least a public service that was in a natural monopoly that will never be correctly managed under private ownership. The most famous example are our highways. State funded, then the exploitation was privatized. It's now expensive as hell, generates 60% of profit that ends up in the pocket of private companies instead of the state.
On top of this kind of economical ultra-liberalism that we're all culturally against pretty much in France, and empirically against if I can say, we have an ideological problem with the decisions that he government takes since decades. To make it short, it's always gifts to public companies or ultra-rich people, while continuing piling up taxes on the poor. Macron, because it's pretty recent, gave what was called the CICE to french companies, that cost around 60 Billions to the economy, at the condition that they were going to use it by job creation, and overall "trickling it down". The president of the french corporate lobby was fiercely wearing "1 million jobs" badge during the different discussions, because he promised 1 million new jobs at the end of the CICE. The last studies showed that the actual result of the CICE was a creation of between 0 and 250 000 jobs, and that's the generous margin.
While I could continue examples of stupid economic politics in favor of a few loaded people, I'll stop this example here to go on another rant concerning our democratic system.
French democratic system is representative. That means that people vote for other people to represent them in the government. And don't really take parts themselves in the democratic process. Experience has shown that this was indeed an aristocracy, since all representatives don't come from the people, because campaigning for a place in parliament is expensive, and you also need a network and friends in high places, so most of them come from the same class.
That leads to people taking decisions that are completely ignoring real life of common people, not measuring any impact, while also generously serving their own personal interests. A whole lot of corruption keeps getting revealed day after day, since decades, and people can't really do anything about. Even in good faith, these people didn't evolve in their life with "normal" people. They stayed in their own social class, and can't relate to the life of people living with minimal wage, or living in the countryside, or just having a normal job having a median pay. They are part, for most of them, of the 1%, and can't really realize what normal people go through because they're the product of their environment.
We also have a president that has a strong role in the politic of our country. The election system that we have is, in my opinion, one of the worse. It has 2 elections, a first one where you vote for the candidate you feel the closest to, and a second one that plays between the 2 most voted of the first vote. Let's be honest, while it's not as bad as the bipartisan system that the US has, it's not that far off. You get spread votes in the first vote, usually best you can get is 25% of votes in first turn, which is what happened in our last elections. We had 4 to 5 candidates with really close results in term of votes. Second elections, you get Macron vs Le Pen which is the far right leader in french politics. People, in France, pretty much never vote "for" a candidate in the second election, but "against" one. In this case, most people voted against the extreme right, but not really because they liked Macron.
So now we get a president that something around 25% of voters wanted (abstention because people don't really believe in our system is kind of high also), and that is also applying a program that is far much on the right side of the compromise he was publicly announcing that he was going to make.
People feel betrayed, feel that their opinion don't matter, and feel that the people that can change that have a conflict of interest in changing these matters. This is why it is the 12th week that people are in the street. This is also why most protester are also converging towards a common cause: the RIC (Citizen Initiative Referendum), that could make citizens able to propose laws, abrogate laws, revoke politicians or modify our constitution. All changes that people want could be proposed using this new tool, which is why a change in our system is now the first thing that people request during the protest.
I won't talk about he media propaganda around this event, or the repression of the protests in this post becuase this is yet another sensitive subject, but I wanted to provide at least a bit more context.
TL;DR : No, this is not about gas price. This is about fiscal injustice, and a poor representation of the interest of the citizens in our current political system and/or corruption. Also Macron keeps insulting the common people so that doesn't help I guess.