I got this game a few days ago and I love it!
I am now up to mission 18 (Check Mate) and I need help. This is the first mission that you get money and NO oil rigs until you capture some.
I get wiped out before I can capture a single oil rig.
If anybody can tell me what troops to buy and what strategy to follow, I would appreciate it.
I'm sure you have probably figured this out, but just in case I'll give you some tips on the easiest way to succeed. The mission starts you off with 1 Engineer and you have to capture the enemy base. I initially buy 2 snipers, 2 Grenadiers, and 1 more Engineer. The trick is to try and take over the training barracks in the top right. You can do this with little or no loss if done right. I use both engineers to quickly convert the barracks in one move, this still leaves one left in which you can capture the oil rig next to that same barracks.
The best way to proceed to the enemy base is to now proceed behind that 'main' street wall. Basically just straight left from the captured barracks. You can create another Engineer from this captured barracks and some cheap Grunts when needed. Using your Granadiers on the higher back wall give you greater distance for the grenades too.
Hopefully this has been helpful to you. If not, then perhaps someone else will find it of use.