Foreign stocks represent an attractive option for investors who wish to diversify their portfolios. However, these equities carry their own special risks, ranging from currency-related to political, and can pose liquidity and due diligence problems for retail investors. Index mutual funds that are global in scope and follow a passive investment approach provide cost-effective means of investing overseas. Here are four of the top performers. All info is current as of November 2018.

Fidelity Spartan International Index Fund Investor Class

2015-2018 average annualized net asset value (NAV) return: 3.8%

Net expense ratio: 0.17%

The Fidelity Spartan International Index Fund Investor Class tracks the performance of the MSCI Europe, Australasia, Far East Index (EAFE), which is a broad index that represents the performance of foreign developed-market stocks. The fund uses sampling techniques to attain investment results similar to those of the underlying index. European stocks have the largest allocation at 66%, while Japanese equities account for about 23% of the fund's assets. The fund provides large exposure to financial and consumer discretionary stocks, which have 25 and 13% allocations respectively. The fund's portfolio is widely diversified; its top 10 holdings account for only about 11% of its assets.

The Fidelity Spartan International Index Fund offers a diversified international portfolio at a very low cost. Because the fund avoids emerging market equities, its returns are subject to lower volatility. Morningstar has awarded the fund a silver analyst rating and a four-star overall rating. The fund is free of load fees and has a minimum investment threshold of $2,500, $200 for IRAs.

Schwab International Index Fund

AUM: $4.3 billion

2015-2018 average annualized NAV return: 3.7%

Net expense ratio: 0.06%

The Schwab International Index Fund also seeks to track the performance of the MSCI EAFE Index. This fund has a very similar asset allocation to its Fidelity Spartan rival. However, the fund weights its assets slightly more in favor of consumer defensive stocks. Like other international equity stocks, the fund exposes investors to foreign currency fluctuations.

The fund has one of the lowest net expense ratios among its peers and an exceptionally low turnover ratio of just 3%, making it highly tax efficient. Morningstar has awarded the fund a bronze analyst rating and a four-star overall rating. The fund has no load fees and comes with a minimum investment requirement of just $1.

Pax MSCI EAFE ESG Leaders Index Fund Individual Investor Class

AUM: $577 million

2015-2018 average annualized NAV return: 2.45%

Net expense ratio: 0.8%

The Pax MSCI EAFE ESG Leaders Index Fund (formerly the MSCI International ESG Index Fund) tracks the performance of the MSCI EAFE ESG Index, which is a member of the MSCI Global Sustainability Indexes. The index provides exposure to companies with high environmental, social and governance performances relative to their sector peers. The fund's portfolio consists of a mixture of large- and mid-cap foreign stocks with high geographical concentration in the United Kingdom and Japan. About 20% of the fund's assets are allocated to financial stocks, while industrials have a 13.5% allocation and health care equities have an 11% allocation.

Morningstar has given the fund a two-star overall rating. The fund does not charge load fees and comes with a minimum investment requirement of $1,000.

Vanguard Developed Markets Index Fund Admiral Shares

AUM: $102.7 billion

2015-2018 average annualized NAV return: 9.82%

Net expense ratio: 0.07%

The Vanguard Developed Markets Index Fund tracks the performance of a benchmark index that measures the investment return of stocks issued by companies located in Canada and the major markets of Europe and the Pacific region. In 2014, Vanguard merged two of its foreign equity funds to form the Vanguard Developed Markets Index Fund. The fund has an exceptionally low turnover ratio of 3.4%, making this fund very tax efficient for its investors. The fund mainly invests in large- and mid-cap stocks of developed markets in Europe (53.5% of the holdings) and the Pacific Rim (37%).

For its very low expense ratio, consistent management and return, the fund has earned a gold analyst rating and a four-star overall rating from Morningstar. The fund charges no load fees and requires its investors to contribute at least $3,000.