Does a 1991 Infiniti G20 come with a v4 or a v6? Or would I have to check with the seller?

I am really concerned about gas, and I know someone who's selling it for $900.

Is it worth buying?

I believe it is a 2.0lt 140hp 4 cylinder. It is basically a gussied up Nissan Sentra. It was well reviewed in its day and was basically reliable. Figure 23-25 mpg in town, and 30+ on the hwy.

For $900, you are not likely to do much better for the money, and some parts are shared with a Sentra, so they should be readily available used.