Overnight High / Low (ONH / ONL)
The high and low printed by S&P 500 futures between the 6:00 PM ET reopen and the 9:30 AM ET cash open — the overnight Liquidity Pools the regular session opens into.
The Overnight High (ONH) and Overnight Low (ONL) are the extremes printed by the E-mini S&P 500 future (ES) during the Globex session, from the 6:00 PM ET reopen to the 9:30 AM ET cash open. Positions opened overnight protect themselves with stops just beyond these edges, so they become Liquidity Pools the moment the regular session opens.
Why they matter at the open: the first hour frequently goes to one overnight edge before it commits. A run above the ONH that closes back inside is a classic opening Liquidity Sweep; a clean break that holds is Acceptance and often starts a directional day.
The honest SPX context: SPX is a cash index and does not trade overnight, so it has no overnight high or low of its own. SPXXL takes the ES Globex session and shifts it by the ES-to-SPX basis so the levels line up on the SPX chart. That makes ONH / ONL an ES proxy, and it is labeled as one wherever SPXXL shows it.
For 0DTE traders: treat the overnight edges as the first two places the open is likely to test. Do not chase the first push into them; watch whether they are swept or accepted, then express a confirmed read with a defined-risk vertical debit spread.
This entry is educational and uses SPX for illustration — it is not financial advice, and no outcome is predicted or guaranteed.
Related Terms
The high and low of the prior regular session — the most-watched levels on any intraday chart, and the most common place stops cluster.
A cluster of resting stop orders sitting just beyond an obvious level — the fuel large players need to fill size. A location, not a signal.
A session where price probes beyond key levels to trigger clustered stop-loss orders before reversing — designed to trap directional traders.
When price closes through a level and holds there — the market agrees to trade at the new price, so the level is spent as a Liquidity Pool.
The price range established during the first 30 minutes of trading (9:30-10:00 AM ET) — a key reference for the entire session.