As Fidelity Investments has become the largest U.S. manager of mutual funds and provider of 401(k) accounts, the Boston-based firm has attracted customers with its one-stop financial-services model, counting 24 million individual and institutional clients with $1.4 trillion under management. As its funds go, so does the wealth of many Americans.

TheStreet.com Ratings has been reviewing the best-performing Fidelity stock mutual funds so far this year.

The Fidelity fund with the highest return through Feb. 9 was the

Fidelity Select Natural Gas Portfolio

(FSNGX) - Get Report

, which jumped 13.6%. Of the company holdings focusing on exploration, transmission, distribution and other services related to natural gas, standouts include

Tesoro

(TSO)

, with a gain of 40.3%;

PetroHawk Energy

(HK)

, with an advance of 38.3%; and

Transocean

(RIG) - Get Report

, with an increase of 28.6%.

The second-best-performing fund was the

Fidelity Select Medical Delivery Portfolio

(FSHCX) - Get Report

, gaining 10.9%.

UnitedHealth Group

(UNH) - Get Report

and

Medco Health Solutions

(MHS)

dominate the fund, accounting for 17.2% and 11.2% of assets, respectively. Of the noteworthy holdings,

Cigna

(CI) - Get Report

appreciated 32%, and

Aetna

(AET)

climbed 20%. Medco Health Solutions rose 13.2%, and UnitedHealth Group returned 11%.

While none of those funds contributed to Fidelity's victory in the

"Ultra" Fund Family

competition, they remain funds to watch for potential upgrades if they are able to sustain their momentum over the next few months.

Source: TheStreet.com Ratings. Read

this

for an explanation of our ratings.

Kevin Baker became the senior financial analyst for TSC Ratings upon the August 2006 acquisition of Weiss Ratings by TheStreet.com, covering mutual funds. He joined the Weiss Group in 1997 as a banking and brokerage analyst. In 1999, he created the Weiss Group's first ratings to gauge the level of risk in U.S. equities. Baker received a B.S. degree in management from Rensselaer Polytechnic Institute and an M.B.A. with a finance specialization from Nova Southeastern University.