Call walls and put walls: where the open interest lives

Open interest is public. Every strike on the chain shows how many contracts are outstanding, and the distribution is lumpy: a few strikes hold far more than the rest. The largest call strike above price is usually called the call wall; the largest put strike below is the put wall.

Why price slows there

A strike with heavy open interest is a strike where hedging is heaviest. As price approaches it, the dealers holding the other side of those contracts have to adjust, and in a long-gamma regime that adjustment leans against the move. The first approach to a wall often stalls. It is not a wall in the physical sense; it is a place where a lot of flow happens to be pointed the other way.

When a wall gives

Walls are made of positions, and positions change. If price closes through a call wall, the contracts behind it are now in the money, hedging behaviour changes, and the level that was a ceiling can become a reference for support instead. The same is true in reverse for put walls. A wall that is broken and then defended from the other side is a common and useful pattern to recognise.

Reading them honestly

Two cautions. Open interest updates overnight, so a wall computed at 9:30 describes yesterday’s positioning until the day’s volume rebuilds it. And a wall far from price is mostly decoration; the ones within the day’s expected move are the ones that matter.