You may be surprised to learn that, by at least one key measure, the biggest of the world's energy companies isn't ExxonMobil (NYSE:XOM) or Royal Dutch Shell (NYSE:RDS-A) (NYSE:RDS-B) or Chevron (NYSE:CVX). Indeed, the big enchilada (or maybe big borscht) of public oil and gas is Russia's massive natural gas producer and distributor, Gazprom (OTC BB: OGZPY).

The measure I'm using in my ranking is the amount of capital being spent to uncover new oil and gas reserves. At Gazprom, which supplies about 40% of Europe's natural gas needs -- something that should make your geopolitical knees knock -- the capital budget has been doubled this year to about $30 billion. That’s a lot of rubles, and compares to $27 billion at Shell, with both BP (NYSE:BP) and Exxon in the low $20-billion range.

And now for your second surprise: Those numbers probably indicate that the companies are actually shrinking faster than yours truly on his new diet. In Gazprom's case, the spending is being ramped -- no, rocketed -- up in hopes of compensating for depletion in the company's Siberian fields, a phenomenon that's occurring in the face of a sizable jump in demand for gas in Russia itself.

In Exxon's case, there are a couple of indications of atrophy. First, in a direction that's becoming more the rule than the exception in the industry, the company's oil and gas production slid last year, and on an oil-equivalent basis is below 2003 and 2004 levels. It's therefore similar to most of its peers.

And secondly, Exxon is spending considerably more -- about $32 billion in 2008 -- buying back its stock than it's using to feed exploration and production. Wouldn't you think that, amid skyrocketing oil prices, if finding hydrocarbons weren't becoming more challenging by the day, the company's exploration and production budget would exceed its buyback outlays?

What does all this mean for Foolish investors, especially those eyeing Exxon? You might be surprised yet again to learn that I think it means you'd be well advised to spend some of your shekels on its shares.

While the company's sprung a slow leak, my view is that crude prices will continue to work their way northward, and Exxon's still the biggest publicly traded oil company around by market cap. Beyond that, its buyback budget -- in addition to the $7.6 billion it spends annually for dividends -- can provide a very nice floor under your investment.

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