Oxygen would likely be too expensive to produce for internal combustion to be used (that said a greenhouse effect on Mars would be quite beneficial for terrafor

Oxygen would likely be too expensive to produce for internal combustion to be used (that said a greenhouse effect on Mars would be quite beneficial for terraforming so we might actually figure ways to do that). However the availability of carbon in general and organic materials including complex hydrocarbons will be quite important for local manufacturing of materials such as plastics and composite materials.