Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you expect the global natural resources industry to thrive over time as our developing world keeps demanding building materials and fuel, the WisdomTree Global Natural Resources Index ETF (NYSE: GNAT) could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in a lot of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The WisdomTree ETF's expense ratio -- its annual fee -- is 0.58%. The fund is fairly small, too, so if you're thinking of buying, beware of occasionally large spreads between its bid and ask prices. Consider using a limit order if you want to buy in.

This ETF has underperformed the world market over the past three and five years, but the future matters much more than the past. Also, as with most investments, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver. So, consider how bullish you are about global natural resources in general, and in particular the kinds of companies this ETF invests in.

What's in it?
More than a handful of global natural resources companies had strong performances over the past year. Southern Copper (Nasdaq: SCCO) surged 46%, for example. It carries more debt than many of its peers, but it's investing heavily in capital projects, aiming to boost its production, and it may be able to generate a lot of revenue in copper-hungry China, which has recently announced a $280 billion infrastructure spending plan. Some expect rising demand for copper to be paired with rising prices due to lower inventory levels, too.

Statoil (NYSE: STO), headquartered in Norway, gained 25%, benefiting from higher prices for its Brent Crude oil than the West Texas Intermediate oil produced in the U.S. It also boasts new exploration opportunities, and bulls like how it's getting more efficient, boosting its oil recovery rate. Its revenue and earnings growth rates have been accelerating, as well. With a recent 3.5% dividend yield and a P/E ratio near six, it seems rather attractive.

ConocoPhillips (NYSE: COP) advanced 24% and sports an even higher dividend yield than Statoil, recently yielding 4.6%. The company has been adjusting its focus, shedding some assets and looking into promising new arenas such as fracking opportunities in China. Some analysts have downgraded the company, worrying about the sustainability of its dividend, though its payout ratio is rather reasonable. Other analysts see it as undervalued. It has been buying back a lot of stock -- more than $3 billion worth in the past quarter. It carries a lot of debt, but has been gradually paying that down.

U.K.-based giant BP (NYSE: BP) added 22%. The company has been tackling debt repayment and its legal liabilities from the big 2010 Gulf of Mexico spill by selling off assets to raise money. The U.S. government is reportedly looking for at least $18 billion from BP. Meanwhile, its production has been falling over the past few quarters, leading some analysts to downgrade it. Bulls like its investments in wind power and biofuels, though, as well as its rising dividend -- which recently yielded 4.5%.

The big picture
Demand for global natural resources isn't going away anytime soon. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.

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