I've only ever seen oil below $80 per unit. Which makes sense according to supply and demand. This is a very infantry heavy time and they demand half the oil when compared to food. It only makes sense that oil is a bit cheaper. Once more ships are around I'm sure prices will go up as the demand increases.
Edit: Also, I honestly believe the mins/maxes should be decreased/increased in the public market. Some goods sell instantly at their max price and have no room to find their actual worth to people.