Find the "config.txt" file in the main game directory and open it. Here you can change the costs of all products.
Furthermore, by finding the following line, you can change the amount of money you start with at respectively the easy, medium, and hard difficulties :
To get free items, look for the following words in the file and set the values in front of them to "0":
kaufkosten monatkosten
Unlimited money
During game push control,alt,and shift
Stop time but still get money
You have to be in real time mode to use this. when you get enough oil stored just send a tanker to one of the places and then hit escape and go to the options menu and your tankers will still be moving but time will stop so no days go by.