Natural resources mutual funds, a losing sector in recent years and having lost a net $317 million in assets last year, are some of this year's strongest performing funds. They are being used by at least one fund company to drive sales.

Invesco of Denver earlier this year added its Energy Fund to a company program that aggressively markets 10 to 12 of the firm's strong-performing funds, said Tom Pellowe, a vice president and national account manager with the firm. The list of funds known as "Focus Funds," are used by the company to generate sales and gain market share, he said.

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