Investing.com - With more investors opting for low-cost investment vehicles, the major fund companies are jockeying for advantage by lowering or even eliminating fees.The latest salvos in the fee war are from two long-standing industry giants--Vanguard Group and Fidelity Investments. As of August, Vanguard is offering unlimited, free trading in some 1,800 exchange traded funds. The no-commission policy applies to virtually all of the ETFs on Vanguard's online platform, with the exception of leveraged or inverse funds. Meanwhile, Fidelity is the first company to offer no-fee index funds, which already carry some of the lowest costs in the industry.Thus far, the offer is limited to two equity funds, one domestic and the other international.Investors have been gravitating to passively-managed index funds and ETFs, whose costs are significantly lower than the traditional actively-managed mutual fund.The amount of money invested in U.S. ETFs surged more than 34% in 2017 to a record $3.42 trillion, according to research firm ETFGI.