From Desert Operations Wiki
There are 6 different resources in the game:
Oil, Diesel and Kerosene are needed to attack other players and this is why they are put in the same category (they form a whole resource called fuel). Oil is a scarce resource within the game, so a good advice is to invest in Oil Refineries to have enough of it. Except from diamonds, you'll receive resources every 10 minutes (this is called a tick). The quantity you receive will depend in how many buildings you have that work the production of their respective raw material. Diamonds can also be used to improve and get more resources. The total amount you receive from buildings can be seen under the “Income + Expenses”.