It really is pretty simple. One other trick I use to make it even simpler is coming up with a price to use for reserves in the ground. That number will change with oil prices. So with a $50 oil price I use $5, with $60 oil I use $6, with $70 oil I use $7, etc. Oil is about $80 now so I used $8. Using this, the only real variable is the amount of reserves.
Painfully simple. And best of all, you don't even need a spreadsheet. LOL.
Market Data 
Markets 
AI
