HexCheat:

 How to get enough oil:

 Begin a level and then save the game. Use the hex editor and load the
 saved game.

 In the Survivors levels the first line of your hex will look something
 like this:-

 000000 0100 0000 0000 0000 0000 0000 0000 0000

 Regardless of the numbers that may be in your saved game change this
 to:

 000000 0100 0000 0000 0000 F301 F301 F301 0000

 This will give you over 32 million oil credits.

 In the Mutants levels your hex will look something like this:-

 000000 0200 0000 0000 0000 0000 0000 0000 0000

 Change this to:

 000000 0200 0000 0000 0000 0000 FFFF FFFF FFFF

 This will give you a negative oil figure with the result that you
 will never run out of oil credits.