Oil and gas exploration has taken off this year, amid mutterings of phrases like "peak oil" and "solar power." Analysts estimate that the top independent oil and gas producers spent between 13% and 15% of their capital spending on exploration, up from 8.6% in 2005. The spending has paid off, and discovery after discovery should prompt investors to check out the best E&P outfits as potential investments.

The top 10
Platts Energy recently ranked the top 250 energy companies; the list below is composed solely of the top tier of oil and gas exploration and production companies from those rankings.

Rank

Overall Platts 250 Rank

Company

Assets

Revenue

ROIC

1 15 CNOOC (NYSE: CEO) $50.5 $27.3 24%
2 21 Oil and Natural Gas Corp. $42.8 $25.9 18%
3 46 Apache (NYSE: APA) $43.4 $12.1 9%
4 52 Devon Energy (NYSE: DVN) $32.9 $9.9 10%
5 54 Tatneft $20.3 $15.7 11%
6 62 Bashneft $15.0 $13.3 13%
7 66 Chesapeake Energy (NYSE: CHK) $37.9 $9.4 6%
8 71 Canadian Natural Resources (NYSE: CNQ) $44.1 $12.7 5%
9 76 Inpex $33.0 $11.3 5%
10 87 Encana (NYSE: ECA) $35.2 $8.8 5%

Source: Platts. Dollar figures are in billions.

It's no surprise to see CNOOC at the top of this list. The Chinese company posted a great return on invested capital and is tops in assets and revenue. Chesapeake is surprisingly low on the list. The second largest natural gas producer in the States, it could only muster the second-lowest revenue of the 10 companies listed here.

This list is indicative of the global parity in the oil and gas sector right now, showcasing companies from China, India, Russia, and Japan, as well as the U.S. and Canada.

One more to watch
Anadarko Petroleum (NYSE: APC): The company ranks 15th on the Platts list of E&Ps, and 116th overall. The third largest natural gas producer in the U.S. behind Chesapeake and ExxonMobil (NYSE: XOM), Anadarko just announced a major oil find in Colorado. Early estimates from the discovery in the Wattenberg play are coming in at more than a billion barrels of recoverable oil and natural gas.

No E&P left behind
The integrated majors are finding their exploration mojo as well. Eni (NYSE: E), Statoil (NYSE: STO), and Repsol have all made huge discoveries in recent months. Overall, it's estimated that by 2015 35% of oil majors' assets will be in plays where production is holding steady or increasing, compared with just 20% six years ago.

Foolish bottom line
Once you've identified some solid E&P investments, take it the next step forward. Every exploration and production company needs an oil field service company to assist in the development of new discoveries -- The Motley Fool's special free report "The Only Energy Stock You'll Ever Need" recommends one such company. Click here to check it out!

Fool contributor Aimee Duffy doesn't own shares of the companies mentioned in this article. If you have the energy, check out what she's keeping an eye on by following her on Twitter, where she goes by @TMFDuffy.

The Motley Fool owns shares of Devon Energy. Motley Fool newsletter services have recommended buying shares of Chesapeake Energy and Statoil A. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.