You buy properties, drill for oil, link properties with pipelines so as to collect royalties and try to be the richest player. Event cards complicate matters. Drilling is resolved with a little rig whose plunger is pushed up if it doesn't go through the hidden disc; if it pushes through all three, the well is dry. Deeper holes cost more, of course.
Pipelines can be bought once you have 4 producing oil wells on a property; they reach across that property's boundary to another player's property, and are used to siphon royalties from him every turn. This is a clever mechanic that accelerates bankruptcy and keeps total playing time within reasonable limits.
Once all players but one are pushed into bankruptcy, the remaining one is the winner.