Among popular oil and gas mutual funds for investors to consider, some of the best performing funds, as of January 2015, are Vanguard Energy Fund Investor Shares (VGENX), Fidelity Select Natural Gas Portfolio (FSNGX) and ProFunds Oil Equipment Service and Distribution Fund Investor Class (OEPIX).

Vanguard Energy Fund Investor Shares seeks long-term capital growth. This mutual fund invests in companies' stocks that engage in production, marketing or research of energy. Some of the companies included in this fund seek new uses for traditional energy sources, such as oil and coal. Top holdings of the fund include Exxon Mobil and Chevron. This fund selects stocks to invest in based on analysis of a company’s fundamental value determined by analyzing cash flow and the worth of assets. Nearly all of the fund’s net income is distributed to its shareholders. The fund has a relatively low expense ratio of 0.37%.

Fidelity Select Natural Gas Portfolio is a mutual fund that invests in natural resources with a primary objective of capital appreciation. Typically, at least 80% of the fund’s assets are invested in the common stocks of companies that produce, transmit and distribute natural gas, along with companies that provide services and equipment to producers, refineries and distributors. Top holdings of the fund include Devon Energy, Marathon Oil and Chesapeake Energy. The fund's expense ratio is 0.83%.

ProFunds Oil Equipment Service and Distribution Fund Investor Class is an index mutual fund that seeks daily investment results 1.5 times that of the daily performance of the Dow Jones U.S. Oil Equipment, Services and Distribution SM Index. The fund makes investments in securities and derivatives whose combination should produce such a result. Top holdings of the fund include Schlumberger and Kinder Morgan. The expense ratio for the fund is relatively high at 1.78%.