Fluorinated Silicone or Viton.

These will save you a lot of headache and maybe even more money. If you have any intentions of running a little alcohol or "unusual" fuel additives like toluene a normal Buna-N O-ring may not hold up. It's not just your injector O-rings either, your fuel tank and sender seals can be eaten up, so if you get the chance upgrade and potentially avoid pulling pieces of dissolved rubber out of your fuel system.

 

O-rings: Parker Hannifin O-Ring Handbook

 

Here's an Interesting fact many don't know, Viton is a brand name https://en.wikipedia.org/wiki/Viton

 

Viton IS well known as a brand name, but like many, has become "unbranded" by common usage, like Jello and Kleenex.