[manpower]

I'm not really sure what answer you're looking for, and I think you should just go ahead and post your side to the argument you've had, but I'll point out something that no one has bothered to say yet:

Non-repleneshing natural resources, namely oil, are limited and will eventually run out. This is important because if you assume a]that oil will continue to increase in value and b]that the company has a pretty good idea exactly how much oil they have in their specific field. It's possible (though by no means certain) that it will be a good idea for them to NOT invest.

Here's an example of when the above would be true. If an investment affects only production capacity (not efficiency or cost of extraction). It is not in the company's best interest to boost production when the time-value of a large expenditure on say, a new drilling platform, would be less profitable than an alternative investment, namely, leaving the oil in the ground until it's worth $200 a barrel and investing the money in t-bonds until then.