SPDR S&P 500 ETF Trust (SPY) remains the largest U.S. equity ETF by assets under management, with more than $380 billion invested as of year-end. Launched in 1993, SPY pioneered index-tracking ETFs and continues to account for roughly 15% of total S&P 500 ETF flows. Its broad institutional and retail adoption offers deep exposure to the 500 largest U.S. companies, making it a bellwether for passive equity investing.

SPY trades an average daily volume exceeding 80 million shares, outpacing all other equity ETFs and resulting in bid-ask spreads typically below one basis point. This exceptional liquidity supports ultra-tight execution for traders and institutions executing large blocks. In contrast with newer, lower-cost competitors, SPY’s market depth helps minimize trading slippage during periods of heightened volatility.

Despite its trading advantages, SPY carries an annual expense ratio of 0.0945%, more than triple that of rival ETFs such as Vanguard’s VOO. While the extra 0.06% fee may be imperceptible for high-frequency traders or short-term strategies, long-term buy-and-hold investors could see fee drag compound into a 5–10% reduction in net returns over a decade. Investors weighing SPY against lower-cost alternatives should consider trading frequency, tax treatment of distributions, and portfolio turnover before committing to its slightly higher fee structure.