Launched on 05/01/2006, the iShares U.S. Oil & Gas Exploration & Production ETF (IEO) is a passively managed exchange traded fund designed to provide a broad exposure to the Energy - Exploration segment of the equity market.An increasingly popular option among retail and institutional investors, passively managed ETFs offer low costs, transparency, flexibility, and tax efficiency; they are also excellent vehicles for long term investors.Sector ETFs are also funds of convenience, offering many ways to gain low risk and diversified exposure to a broad group of companies in particular sectors. Energy - Exploration is one of the 16 broad Zacks sectors within the Zacks Industry classification. It is currently ranked 12, placing it in bottom 25%.Index DetailsThe fund is sponsored by Blackrock. It has amassed assets over $317.19 M, making it one of the larger ETFs attempting to match the performance of the Energy - Exploration segment of the equity market. IEO seeks to match the performance of the Dow Jones U.S. Select Oil Exploration & Production Index before fees and expenses.The Dow Jones U.S. Select Oil Exploration & Production Index is a free-float adjusted market capitalization-weighted index. The Index includes companies that are engaged in the exploration for and extraction, production, refining, and supply of oil and gas products.CostsInvestors should also pay attention to an ETF's expense ratio. Lower cost products will produce better results than those with a higher cost, assuming all other metrics remain the same.Annual operating expenses for this ETF are 0.43%, making it one of the cheaper products in the space.It has a 12-month trailing dividend yield of 1.68%.Sector Exposure and Top HoldingsEven though ETFs offer diversified exposure which minimizes single stock risk, it is still important to look into a fund's holdings before investing. Luckily, most ETFs are very transparent products that disclose their holdings on a daily basis.This ETF has heaviest allocation in the Energy sector--about 100% of the portfolio.Looking at individual holdings, Conocophillips (COP) accounts for about 14.44% of total assets, followed by Eog Resources Inc (EOG) and Marathon Petroleum Corp (MPC).The top 10 holdings account for about 65.73% of total assets under management.Performance and RiskThe ETF has lost about -19.92% so far this year and is down about -20.45% in the last one year (as of 12/31/2018). In that past 52-week period, it has traded between $47.66 and $78.42.The ETF has a beta of 1.27 and standard deviation of 27.73% for the trailing three-year period, making it a high risk choice in the space. With about 70 holdings, it effectively diversifies company-specific risk.AlternativesIShares U.S. Oil & Gas Exploration & Production ETF carries a Zacks ETF Rank of 3 (Hold), which is based on expected asset class return, expense ratio, and momentum, among other factors. Thus, IEO is a good option for those seeking exposure to the Energy ETFs area of the market. Investors might also want to consider some other ETF options in the space.VanEck Vectors Unconventional Oil & Gas ETF (FRAK) tracks MVIS Global Unconventional Oil & Gas Index and the SPDR S&P Oil & Gas Exploration & Production ETF (XOP) tracks S&P Oil & Gas Exploration & Production Select Industry Index. VanEck Vectors Unconventional Oil & Gas ETF has $49.37 M in assets, SPDR S&P Oil & Gas Exploration & Production ETF has $2.24 B. FRAK has an expense ratio of 0.54% and XOP charges 0.35%.Bottom LineTo learn more about this product and other ETFs, screen for products that match your investment objectives and read articles on latest developments in the ETF investing universe, please visit Zacks ETF Center.Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report ISHARS-US O&G (IEO): ETF Research Reports SPDR-SP O&G EXP (XOP): ETF Research Reports VANECK-UNC O&G (FRAK): ETF Research Reports Marathon Petroleum Corporation (MPC): Free Stock Analysis Report EOG Resources, Inc. (EOG): Free Stock Analysis Report ConocoPhillips (COP): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research