Every StaxInvesting article tagged liquidity · 3 posts.
3 articles
In under a decade, same-day options went from a Friday-only quirk to the majority of SPX options volume. That was not an accident of retail enthusiasm. It was the result of a specific market-structure change, the rollout of daily expirations, meeting expanded retail access and a self-reinforcing dealer-hedging feedback loop. Here is the actual mechanism behind the explosion, and what the numbers do and do not say.
SPX and XSP are the same index, the same settlement, the same tax treatment, and the same exercise style. The only real difference is size: XSP is one-tenth the notional. That makes the choice between them almost entirely a question of account size, with one liquidity catch that trips up the exact traders XSP was built for. Here is how to choose, now that the elimination of the PDT rule has made small-account intraday trading far more common.
0DTE options on SPX and SPY look highly liquid, and at the money they genuinely are. But the surface picture hides three things that cost real money: spreads that widen away from the money and late in the session, displayed size that barely reflects true liquidity, and fills that blow out catastrophically in exactly the fast markets you most need to exit. The through-line is slippage, the hidden cost that makes a profitable backtest an unprofitable strategy.
