Yes, it is possible. After a certain amount of time in abstinence, you revirginate.

It is my understanding from a "Modern Marvels" show on history channel, that all of the gasoline from the various stations is the same gas, except for a few addatives (done when they fill the tanker truck). Supposedly, they share the distribution system kinda like the electric grid. It may be a different system in different parts of the country. And I realize this contradicts the real-life experiences with different brands of gas reported by users here.