Look under construction and it is not available. I've looked at my base and its not there either. Is there something to upgrade why I don't have an option to 5th Oil Derrick?

No Commander..There is nothing to upgrade..5 oil derricks is standard...There is a possibility that you are experiencing some in game malfunction..but first try clearing your browser and clearing your Cache...Sometimes this is all that it takes..If that does not fix the problem then you will have to contact Support ..Support can access your game and will be able to determine if there is something else going on with your game