I don’t think space travel will ever get to the point of colonizing Mars, because oil is eventually going to get a whole lot more expensive due to the aggregate production rate of oil fields, not oil depletion, which it is often confused with.

The world has a high dependence on oil. It used for transport, agricultural and industrial systems. (Beyond Oil: The View from Hubbert’s Peak by Deffeyes, Kenneth S.)

We have 50% of the oil left, but it gets more and more expensive to extract to get the rest of it, meaning the price will have to go up and up. Hydraulic fracking has bought us some time, however. That’s why there’s that peak again at the end of the graph.

Fracking has been performed worldwide on oil, half of which have been done in the U.S.

Also, it’s probably terrible for the environment. It possibly causes: “ground and surface water contamination, air and noise pollution, and triggering earthquakes.” (Source)