Ms. Sullivan's focus on fast-growth companies and industries has resulted in a concentrated fund.

"If there's good stock selection," he explained, "a concentrated fund has the opportunity to significantly outperform the market."

Over a much longer period, however, the concentrated funds come out slightly ahead.

Alternatively, some managers of concentrated funds that did own energy stocks have seen their funds gain ground.

But some smaller or more concentrated funds got a bigger boost from the deal.

"That's the trait of a concentrated fund - it can lose ground rapidly and make it up quite quickly."

Like Focus Twenty, most of the concentrated funds sank last year with the collapse of technology stocks.

A concentrated fund suffers a bigger decline than a more diversified fund if a single position turns sour.

Examples are some of the new concentrated funds, which invest in the top 20 or 30 picks of a manager with a good track record.

Compare that figure with the 10.1 annualized gains of concentrated funds with 30 or fewer stocks.