Chains, Spreads and Liquidity

What the chain is telling you

An option chain is a grid of strikes down one side and expiries across the other, and each cell carries four numbers: the bid, the ask, the volume and the open interest. Only the first two are prices; the other two describe whether a market exists. Open interest is the number of contracts outstanding at that strike and expiry, and it is the best available proxy for depth — a strike with thousands of contracts outstanding has market makers quoting it because there is flow to earn from, while a strike with forty contracts outstanding may have a nominal quote and no interest in trading size. Volume is what changed hands today, which tells you about activity rather than depth: a strike can show heavy volume and no open interest if everyone opened and closed within the session. The bid/ask is the cost of entry and exit, and it is quoted in a unit that makes the comparison honest: the spread as a percentage of the mid-price or of the premium. A five-cent spread on a $0.20 option is 25% of the premium, which is enormous; the same five cents on a $12.00 option is 4%, which is ordinary. That is why cheap contracts are not cheap: a lottery ticket quoted 0.15/0.20 costs a quarter of its value to enter and another quarter to leave, so the underlying has to move a long way before the position is even level. The same logic scales to structures: a vertical spread has two legs, so it is crossed twice on entry and twice on exit, and the friction is charged against the *width minus the debit* — the smallest number on the ticket. On a $5 width with a $3.30 debit, the maximum profit is $1.70, and $0.30 of round-trip friction is nearly a fifth of it. Depth also appears in the size that can be quoted rather than just the price. A market maker who will trade fifty contracts at a penny wide may widen dramatically for five hundred, because the inventory risk changes with size. That is why an options position has a size limit that a share position of the same notional does not: the liquidity of the *contract* rather than the liquidity of the stock decides what can be done, and a $500,000 position in a $2bn stock can still be untradeable in an option that only quotes a hundred contracts wide. Reading one row of a chain — Bid / ask: 2.10 / 2.40: Crossing costs $0.30 — 12% of the $2.25 mid ← · Open interest: 8,400: Deep enough for ordinary retail size at a penny or two · Volume today: 310: Activity rather than depth — it says nothing about how much can be traded · Strike spacing $2.50: Wide spacing means coarse choices: fewer structures fit the view · Two-leg structure: The $0.30 toll is charged twice in and twice out, against the width minus debit ← The unit that makes spreads comparable is the percentage of premium or of the structure’s maximum profit. A quoted spread in cents tells you nothing until you divide it by what you are risking.

The pre-trade checklist

Five questions, all answerable before the order goes in. Does an open interest of at least a few hundred contracts exist at the strikes being used? Is the quoted spread small relative to the premium or to the structure’s maximum profit — a common rule of thumb is under 5% for a single leg and well under 20% of the profit for the whole structure? Is the expiry far enough out that the position is not paying for the market’s own gamma while also paying the toll? Are the strikes spaced closely enough that the structure can express the view rather than a nearby approximation of it? And is the size within what the quoted depth can absorb, remembering that closing the position will need the same size again? Two execution habits follow from the arithmetic. The first is to use limit orders priced between the mid and the natural side rather than market orders: because the quoted spread is a negotiation rather than a price, a limit at the mid is often filled, and the improvement is exactly the quantity this lesson measured. The second is to plan the exit before the entry, because a structure that can be opened and not closed is the worst of both worlds — and in practice the exit is the harder side, since the seller of a spread that has gone their way is usually facing a wider spread than when they opened. Both habits reduce to the same rule: the cost is the spread, so anything that reduces the number of times the spread is crossed, or the width at which it is crossed, is worth more than a marginally better view. • Open interest measures depth; volume measures activity. Prefer depth. • Compare the spread as a percentage of the premium, not in cents. • A structure is crossed on every leg, in and out — count the toll against the smallest number on the ticket. • Price entry and exit with limits near the mid rather than paying the natural. • Liquidity constrains the *contract* size, which is why options positions are limited by depth rather than by the stock. The trap that catches experienced traders rather than beginners: a deep, liquid stock with an illiquid option chain. A $50bn company can trade a billion dollars of shares a day while its far-dated $5-wide strikes quote twenty contracts wide, because option liquidity clusters near the money and near the nearest expiries. The underwriting is fine, the idea is fine, and the structure is untradeable at size — which is a liquidity constraint rather than a thesis problem, and it is invisible unless the chain is checked first.

What the quoted spread is made of

The spread is a price for a service, and naming the service explains why it varies so much between strikes of the same name. The market maker quoting the contract takes on an obligation to trade at a price they set, so the width has to cover the cost of laying off whatever exposure the trade leaves behind. That cost is not constant: it is small when the position can be offset immediately in a deep underlying, and large when the contract sits far from the money, runs long-dated, or is exposed to an event that could carry the stock through the strike in a single session. A five-dollar difference in strike can change the dealer’s risk by more than the whole premium, which is why one strike quotes two cents wide and the one beside it quotes forty. Two components are worth separating. The first is the *underlying* risk: a dealer who is short a call is short delta and must buy stock to hedge, and the cost of doing so is what a narrow quote near the money reflects. The second is the *volatility and time* exposure: a far out-of-the-money contract has almost no delta but a great deal of optionality, so the dealer is mostly exposed to a volatility move rather than a stock move, and hedging that in an illiquid strike is expensive or impossible. Add the known events — an earnings date inside the expiry, a dividend, a stock that is hard to borrow — and the width becomes a summary of everything the dealer would have to do to get flat. The width is also not a fixed property of the contract, because an option is quoted on several exchanges at once and the best bid and best offer can come from different venues. What is displayed is a composite, and the true market is the set of quotes rather than the single spread on screen. That is the opening for price improvement: an order expressed at the mid, or a limit between the mid and the natural side, can be filled by a venue the screen is not showing, and the improvement is often a meaningful share of the width. It also means the quote can widen and narrow through a session without the contract changing at all, because dealers retreat around scheduled data and return afterwards. The consequence for sizing and timing is direct. Judge the width against the risk the dealer is carrying rather than against a fixed tolerance: a penny-wide near-dated strike near the money is a place where size and repeated execution are cheap, while a wide far-dated strike is a place where a single round trip may cost more than the thesis is worth. And prefer the moments when the market is functioning — after the open, outside the blackout before a release — rather than the first minutes of the session or the hour before scheduled data, when every quote is a defensive one. • The width pays for hedging: offsetting the trade in the underlying, then laying off the residual volatility and time risk. • Near-the-money, near-dated contracts are cheap to quote; far-dated and far-out strikes are not. • The composite quote is not the market: several venues quote each contract, and the best prices can sit on different ones. • Work orders at or inside the mid to capture price improvement, and give a limit order time to fill. • Quote quality depends on the clock: avoid the open, the close and the minutes before scheduled data. A screen showing a two-cent-wide market is not a promise about the fill for a large order. The size behind each quote is the part that rarely appears on a retail platform, and a hundred contracts can clear a penny-wide market while a thousand cannot — which is why quoted depth is checked as well as quoted width.

Sources

• Option chains, open interest, volume and quoted spreadsCBOE Education — Reading an Option Chain
• Execution costs and liquidity in listed optionsNatenberg, “Option Volatility and Pricing” (liquidity sections)
• Market quality and price improvement in the options marketExchange Rule 605/606 disclosure reporting, as referenced in Markets M22