Investing isn't easy. Even Warren Buffett counsels that most investors should invest in a low-cost index like the S&P 500. That way, "you'll be buying into a wonderful industry, which in effect is all of American industry," he says.

But there are, of course, companies whose long-term fortunes differ substantially from the index. In this series, we look at how individual stocks have performed against the broad S&P 500.

Step on up, Valero (NYSE:VLO).

Valero shares have outperformed the S&P 500 over the past quarter-century, albeit with much more volatility:

Vlo Sp

Source: S&P Capital IQ.

Since 1987, shares have returned an average of 12% a year, compared with 9.7% a year for the S&P (both include dividends). One thousand dollars invested in the S&P in 1987 would be worth $19,200 today. In Valero, it'd be worth $37,200.

Dividends accounted for a lot of those gains. Compounded since 1987, dividends have made up about 70% of Valero's total returns. For the S&P, dividends account for 39% of total returns.

Now have a look at how Valero earnings compare with S&P 500 earnings:

Vlo Earnings

Source: S&P Capital IQ.

Same story here: Good outperformance with much higher volatility. Since 1995, Valero's earnings per share have increased by an average of 16.6% a year, compared with 6% a year for the broader index.

What's that meant for valuations? Valero has traded for an average of 22 times earnings since 1987 -- just below the 24 times earnings for the broader S&P 500.

Through it all, shares have been strong performers over the past quarter-century.

Of course, the important question is whether that will continue. That's where you come in. Our CAPS community currently ranks Valero with a five-star rating (out of five). Care to disagree? Leave your thoughts in the comment section below, or add Valero to My Watchlist

Fool contributor Morgan Housel and The Motley Fool have no positions in the stocks mentioned above. Try any of our Foolish newsletter services free for 30 days. We Fools don't 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.