Investing 102

[MPM IV]

It got quiet in here.

I'm hoping this is a buying opportunity as I'm utilizing money I don't intend to need in the near future.

Since my last post I've added Coke (KO) and Kimber Morgan (KMI) bringing me to a total of six positions. I previously had:

Altria Group (MO)
ATT (T)
Southern Company (SO)
Royal Dutch Shell (RDS.B)

Here is my question for you more knowledgeable and experienced investors. I'm coming to the end of my available funds. RDS has dropped significantly since I invested. Would I be better off creating another position in a different sector, or buying down my price per share of RDS?

I appreciate any insight you gentlemen can provide, but please provide the reason you would do one or the other with your answer.