As anyone who has bought gasoline might guess, the energy/natural resources sector easily outdistanced all other equity mutual fund categories in May.

The average fund in the energy/natural resources sector moved up 7.10% during the most recent month, while the weak U.S. dollar and worldwide economic jitters lifted the average precious metals fund by 6.01% into second place.

Of 17 equity fund actively-managed investment objectives in the accompanying table, all achieved positive returns in May except for the related groupings of financial services, which sank 2.83%, placing it in last place, and real estate, in which the average fund surrendered 0.70%.

The top fund for May in the winning energy/natural resources grouping was

BlackRock Global Resources

(SSGRX) - Get Report

, which vaulted 12.38% during the month. The fund has surged 29.60% for the first five months of 2008 and has enriched investors by 45.69% over the past 12 months. Its largest portfolio holdings include

Consol Energy

(CNX) - Get Report

,

Massey Energy

(MEE)

and

Arch Coal

(ACI) - Get Report

.

Four of the 17 funds that lead their respective investment objectives for May were leveraged, as indicated by the phrase "Ultra" or the indications of "2X" and "2.5X" in their names.

The best performing fund for the month in the adjoining table is the leveraged

ProFunds Ultra Latin America Fund

(UBPIX) - Get Report

, up 18.75% in May and 36.10% year to date. Its largest holdings are

Petroleo Brasileiro (ADS)

(PBR) - Get Report

and

Companhia Vale do Rio Doce ADR

(RIO) - Get Report

.

Although the emerging markets sector was ahead by a middle-of-the-pack 2.42% average pace in May, the grouping's top fund, energy-heavy

ING Russia

(LETRX) - Get Report

, jumped 15.22% for the month to top off a 12-month climb of 47.40%. Its largest holdings are energy giants

Lukoil

and

Gazprom

. The fund is managed by a unit of

ING Groep (ADS)

(ING) - Get Report

.

Richard Widows is a senior financial analyst for TheStreet.com Ratings. Prior to joining TheStreet.com, Widows was senior product manager for quantitative analytics at Thomson Financial. After receiving an M.B.A. from Santa Clara University in California, his career included development of investment information systems at data firms, including the Lipper division of Reuters. His international experience includes assignments in the U.K. and East Asia.