The main sustainability question that must be answered for an oil company like Chevron is what the plan is for continuing revenue when the oil runs out. This is a very long term question, but one that is screaming to be addressed since the fact that the oil will run out is unavoidable.
In order to address it, several other concerns also come into play. How much waste is there in the current production scheme and how does pollution and other problems interfere with current revenues and is that problem likely to become more serious as oil becomes more scarce. Questions about lawsuits or other situations where the company will have to pay for mistakes or unwillingness to comply with environmental regulations all become more important as profit margins shrink and extracting existing oil becomes more and more difficult and costly.
So a plan for long term viability without oil is important and steps that will reduce liabilities and increase margins between now and the end of oil are also vital.