Another way to look at it is:
A company who has 100 million shares & is $1 a share (market cap $100m) is more expensive than a company who has 10 million shares & a share price of $5 (market cap $50).
SEY is currently over 4 times cheaper than SGY. So if they hit a huge oil flow (note the word if, reads posts by sle above) then SEY's share price will go up much more.