Nafta (gas) prices are more expensive than in the US. Avoid común (regular) as it’s usually low quality. Super and premium are better choices. In Patagonia gas prices are about a third less than elsewhere.
Estaciones de servicio (gas stations) are fairly common, but outside the cities keep an eye on your gas gauge. In Patagonia it’s a good idea to carry extra fuel.
A very handy website for those driving around Argentina is www.ruta0.com. Among other things, you can punch in two destinations and get the recommended routes (and whether they’re paved or not), distances in kilometers, driving times and even how much it will cost in gas consumption.