system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What's the difference between "quality" gasoline and "cheap" gasoline?

Everyone talks about "quality" gas like Chevron or whatever and knocks "bad" gas like Arco. What's the difference? Is it worth it? Why?
gpt
The difference is the additives in the gas. For example, Shell sells nitrogen enriched gas that they claim helps eliminate deposits in the engine. They advertise heavily by saying that their gas is fundamentally better.

Independent tests have shown that there is no difference in emissions, fuel economy, or performance. There might have been a difference 30-40 years ago, but all gas has to meet strict government standards. Once gas has met those standards, there isn't much more you can do to improve it.

So the difference is mainly advertising dollars.