Long-term government bond portfolios invest at least 90% of their holdings in bonds backed by the U.S. government or by government-linked agencies. Though these funds are not risk-free, this government backing minimizes the credit risk of these portfolios, as the U.S. government is unlikely to default. Under normal circumstances, these funds tend to have average effective maturities greater than 10 years or durations of more than six years. These three high-yielding, long-term government bond funds did not have any sales loads as of March 2016.

Vanguard Extended Duration Treasury Index Fund (VEDTX)

The Vanguard Extended Duration Treasury Index Fund ("VEDTX") tracks the Barclays U.S. Treasury STRIPS 20-30 Year Equal Par Bond Index, which is an index of extended-duration zero-coupon U.S. Treasury securities. The fund aims to provide high current income with high credit quality. This fund is one of the few extended-duration mutual funds available.

As of March 2016, the fund is invested in 74 individual bonds, all of which are Treasury bonds (T-bonds). The portfolio has an average effective maturity of 25.2 years and an average duration of 24.8 years. The Vanguard Extended Duration Treasury Index Fund holds no short-term reserves. The fund's standard deviation, calculated from trailing 36-month fund returns relative to the associated benchmark, is 17.84%. It has an expense ratio of 0.08%, which is 87% lower than the average expense ratio of funds with similar holdings. As of March 2016, its current 30-day SEC yield was 2.66%. The fund has a minimum investment of $5 million, it was the highest-yielding long-term government bond fund on the market as of March 2016.

Vanguard Long-Term Treasury Fund (VUSTX)

The Vanguard Long-Term Treasury Fund Investor Shares ("VUSTX") invests in long-term debt issued directly by the government. This fund is similar to the Vanguard Extended Duration Treasury Index Fund, but the Investor Shares class of this mutual fund has a much lower minimum investment of only $3,000 and its duration is 17 years, giving it a much lower interest rate risk. It is a suitable and accessible fund for investors seeking interest income who can tolerate high interest rate risk.

The fund is invested in 55 different bonds. T-bonds account for 99.5% of long exposure in the portfolio, government mortgage-backed securities (MBS) account for 0.9% of long exposure and short-term reserves account for 0.4% of short exposure in the fund. While the fund's duration is 17 years, its average effective maturity is 25.3%. The Vanguard Long-Term Treasury Fund Investor Shares has an expense ratio of 0.2%, which is 68% lower than the average expense ratio of funds with similar holdings. As of March 2016, the fund had a 30-day SEC yield of 2.32%.

PIMCO Long-Term U.S. Government Fund (PLGDX)

The PIMCO Long-Term U.S. Government Fund ("PLGDX") seeks to maximize total return and preserve capital by investing in long-term U.S. government securities. The fund is most suitable as a core holding for risk-tolerant investors or to help position a portfolio for expected interest rate trends. The fund's benchmark index is the Barclays Long-Term Treasury Index, which consists of U.S. Treasury issues with maturities of 10 or more years.

The portfolio has an effective duration of 17.29 years and a standard deviation of 10.03%. Bonds with maturities greater than 20 years comprise 78.39% of the portfolio, while bonds with maturities ranging from 10 to 20 years comprise 14.54%. The remaining assets are allocated to issues with maturities less than 10 years. The PIMCO Long-Term U.S. Government Fund's average effective maturity is 24.26 years. The fund is 82.3% invested in U.S. government-related issues, while the remaining assets are allocated to MBS, high-yield and municipal securities. The expense ratio of the fund is 0.875%, and its 30-day SEC yield, as of March 2016, was 1.98%.

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